I've been working on these presentation types, to complete the set.
'%' is straightforward, just multiply the mpf by 100 and add a % sign at the end.

'n' is a lot trickier, since some locales may be difficult to program.
For instance,

>>> import locale
>>> locale.setlocale(locale.LC_ALL, 'en_IN.utf8')
>>> print('{:.10n}'.format(100000.25))
1,00,000.25

Would a partial implementation of 'n' (i.e., only care about thousands and decimal separators) be useful or should we not bother at all with it?