Hi,
Support for snippets is a good and complete topic and affects several Eclipse.org projects, so that's cool to work on it and 7 weeks seems to be a good estimation. But like all estimation, it may as well be way too short or way too long ;) It can also be that with 2 weeks of work, you get a partial support that is already covering the vast majority of cases, and that we decide that some other issues are now more valuable to work on instead of spending 5 more weeks on corner-cases...
What I think would be better candidates are the missing LSP features in LSP4E (like prepareRename). It would be nice if you could cover some of them as part of your GSoC proposal. I don't think you need to sort out the exact features right now and detail them in your proposal (I may be wrong, I didn't read the details); so you could write something like "Once the support for completion snippets and choice is implements, we'll audit LSP4E compliance with the LSP specification, and find out the missing features. Then, depending on the results of this audit, we'll try to implement the most important ones.". Even if you discover 15 missing features and can only implement one, the fact that you open 15 bugs to the project that weren't open before is a valuable contribution that can be highlighted as part of the GSoC.
Cheers,