Proposed resolution:

At the end of 27.9.1 File streams [fstreams] add a paragraph:

In this subclause, member functions taking arguments of const std::filesystem::path::value_type* shall only be provided on systems where std::filesystem::path::value_type ([fs.class.path]) is not char. [Note: These functions enable class path support for systems with a wide native path character type, such as wchar_t. — end note]

Change 27.9.1.1 Class template basic_filebuf [filebuf] as indicated:

basic_filebuf<charT,traits>* open(const char* s,
    ios_base::openmode mode);
basic_filebuf<charT,traits>* open(const std::filesystem::path::value_type* s,
    ios_base::openmode mode);  // wide systems only; see [fstreams] 
basic_filebuf<charT,traits>* open(const string& s,
   ios_base::openmode mode);
basic_filebuf<charT,traits>* open(const filesystem::path& p,
   ios_base::openmode mode);

Change 27.9.1.4 Member functions [filebuf.members] as indicated:

basic_filebuf<charT,traits>* open(const char* s,
   ios_base::openmode mode);
basic_filebuf<charT,traits>* open(const std::filesystem::path::value_type* s,
   ios_base::openmode mode);  // wide systems only; see [fstreams]

To 27.9.1.4 Member functions [filebuf.members] add:

basic_filebuf<charT,traits>* open(const filesystem::path& p,
   ios_base::openmode mode);

Returns: open(p.c_str(), mode);

Change 27.9.1.6 Class template basic_ifstream [ifstream] as indicated:

explicit basic_ifstream(const char* s,
    ios_base::openmode mode = ios_base::in);
explicit basic_ifstream(const std::filesystem::path::value_type* s,
    ios_base::openmode mode = ios_base::in);  // wide systems only; see [fstreams]
explicit basic_ifstream(const string& s,
    ios_base::openmode mode = ios_base::in);
explicit basic_ifstream(const filesystem::path& p,
    ios_base::openmode mode = ios_base::in);
...
void open(const char* s,
    ios_base::openmode mode = ios_base::in);
void open(const std::filesystem::path::value_type* s,
    ios_base::openmode mode = ios_base::in);  // wide systems only; see [fstreams]
void open(const string& s,
    ios_base::openmode mode = ios_base::in);
void open(const filesystem::path& p,
    ios_base::openmode mode = ios_base::in);

Change 27.9.1.7 basic_ifstream constructors [ifstream.cons] as indicated:

explicit basic_ifstream(const char* s,
    ios_base::openmode mode = ios_base::in);
explicit basic_ifstream(const std::filesystem::path::value_type* s,
    ios_base::openmode mode = ios_base::in);  // wide systems only; see [fstreams]

To 27.9.1.7 basic_ifstream constructors [ifstream.cons] add:

explicit basic_ifstream(const filesystem::path& p,
    ios_base::openmode mode = ios_base::in);

Effects: the same as basic_ifstream(p.c_str(), mode).

Change 27.9.1.9 Member functions [ifstream.members] as indicated:

void open(const char* s,
    ios_base::openmode mode = ios_base::in);
void open(const std::filesystem::path::value_type* s,
    ios_base::openmode mode = ios_base::in);  // wide systems only; see [fstreams]

To 27.9.1.9 Member functions [ifstream.members] add:

void open(const filesystem::path& p,
    ios_base::openmode mode = ios_base::in);

Effects: calls open(p.c_str(), mode).

Change 27.9.1.10 Class template basic_ofstream [ofstream] as indicated:

explicit basic_ofstream(const char* s,
    ios_base::openmode mode = ios_base::out);
explicit basic_ofstream(const std::filesystem::path::value_type* s,
    ios_base::openmode mode = ios_base::out);  // wide systems only; see [fstreams]
explicit basic_ofstream(const string& s,
    ios_base::openmode mode = ios_base::out);
explicit basic_ofstream(const filesystem::path& p,
    ios_base::openmode mode = ios_base::out);
...
void open(const char* s,
    ios_base::openmode mode = ios_base::out);
void open(const std::filesystem::path::value_type* s,
    ios_base::openmode mode = ios_base::out);  // wide systems only; see [fstreams]
void open(const string& s,
    ios_base::openmode mode = ios_base::out);
void open(const filesystem::path& p,
    ios_base::openmode mode = ios_base::out);

Change 27.9.1.11 basic_ofstream constructors [ofstream.cons] as indicated:

explicit basic_ofstream(const char* s,
    ios_base::openmode mode = ios_base::out);
explicit basic_ofstream(const std::filesystem::path::value_type* s,
    ios_base::openmode mode = ios_base::out);  // wide systems only; see [fstreams]

To 27.9.1.11 basic_ofstream constructors [ofstream.cons] add:

explicit basic_ofstream(const filesystem::path& p,
    ios_base::openmode mode = ios_base::out);

Effects: the same as basic_ofstream(p.c_str(), mode).

Change 27.9.1.13 Member functions [ofstream.members] as indicated:

void open(const char* s,
    ios_base::openmode mode = ios_base::out);
void open(const std::filesystem::path::value_type* s,
    ios_base::openmode mode = ios_base::out);  // wide systems only; see [fstreams]

To 27.9.1.13 Member functions [ofstream.members] add:

void open(const filesystem::path& p,
    ios_base::openmode mode = ios_base::out);

Effects: calls open(p.c_str(), mode).

Change 27.9.1.14 Class template basic_fstream [fstream] as indicated:

explicit basic_fstream(const char* s,
    ios_base::openmode mode = ios_base::in|ios_base::out);
explicit basic_fstream(const std::filesystem::path::value_type* s,
    ios_base::openmode mode = ios_base::in|ios_base::out);  // wide systems only; see [fstreams]
explicit basic_fstream(const string& s,
    ios_base::openmode mode = ios_base::in|ios_base::out);
explicit basic_fstream(const filesystem::path& p,
    ios_base::openmode mode = ios_base::in|ios_base::out);
...
void open(const char* s,
    ios_base::openmode mode = ios_base::in|ios_base::out);
void open(const std::filesystem::path::value_type* s,
    ios_base::openmode mode = ios_base::in|ios_base::out);  // wide systems only; see [fstreams]
void open(const string& s,
    ios_base::openmode mode = ios_base::in|ios_base::out);
void open(const filesystem::path& p,
    ios_base::openmode mode = ios_base::in|ios_base::out);

Change 27.9.1.15 basic_fstream constructors [fstream.cons] as indicated:

explicit basic_fstream(const char* s,
    ios_base::openmode mode = ios_base::in|ios_base::out);
explicit basic_fstream(const std::filesystem::path::value_type* s,
    ios_base::openmode mode = ios_base::in|ios_base::out);  // wide systems only; see [fstreams]

To 27.9.1.15 basic_fstream constructors [fstream.cons] add:

explicit basic_fstream(const filesystem::path& p,
    ios_base::openmode mode = ios_base::in|ios_base::out);

Effects: the same as basic_fstream(p.c_str(), mode).

Change 27.9.1.17 Member functions [fstream.members] as indicated:

void open(const char* s,
    ios_base::openmode mode = ios_base::in|ios_base::out);
void open(const std::filesystem::path::value_type* s,
    ios_base::openmode mode = ios_base::in|ios_base::out);  // wide systems only; see [fstreams]

To 27.9.1.17 Member functions [fstream.members] add:

void open(const filesystem::path& p,
    ios_base::openmode mode = ios_base::in|ios_base::out);

Effects: calls open(p.c_str(), mode).