More choices for arranging are definitely needed. Translation role for lyrics is also great addition.
I'm personally against freetext field for specifying instruments if it has to be done one by one, here's what I mean -
here we have some 20 or so violin players. It would be... not convenient if we have to type 20 times (even just copy & pasting it, that's way more realistic) for every instrumentalist. And there are other instrument groups. It will be more tolerable if we can tick a checkbox next to the artist (still ticking it 20 times xD) and enter the name of the instrument in freetext field only once and do some sort of apply button that will of course fill out other 19 fields with the same instrument.
Even so, just having the 'Instrumentalist' would be fine, without freetext field. That's not problem when there's just a few instrumentalists, but when
something like Call of Duty comes, happy times....... We still have notes: type "violin" - and 20 names after. Still beats freteext
But that's only a personal opinion.
What happens if we, with the information available, can't specify the roles any further? To stay with the orchestra as an example, sometimes all orchestra players are credited just as 'musicians', so we don't know what instrument they played (except few solo instrumentalists). Can we leave them only as instrumentalists?