Basic morpheme?

["Seppo Kittilä"]

Dear colleagues,

I am sending you this query on behalf of a student of mine, who is not on the list. He is writing his BA (and later his MA) with the working title 'The correlation between basicness/markedness of morphology and phonology from a cross-linguistic perspective'. The idea is to study whether morphemes that express basic functions (such as tense and common cases) are also phonologically basic, meaning that they usually contain cross-linguistically common phonemes, even though language would also have marked and thus rare phonemes. For that he would need studies that have dealt with the basicness of morphemes. Basicness is, of course, a feature that can be defined in numerous ways, but he is interested in morphemes with the following features:

1. They are typologically frequent
2. They are obligatory (i.e. they cannot be dropped) 
3. They are common in speech
4. They express some kind of grammaticalized meaning

So, my question is whether there are any studies on this kind of basicness of morphemes. Many of you know much more about morphology than I do, because of which I thought it is best to send the message to you all.

Your help will be acknowledged. All the best wishes,
Seppo