Hi Sobir,
here's the page with last year's GSoC applications:
https://github.com/sympy/sympy/wiki/GSoC-2017-Current-Applications. And these are the projects that got accepted:
https://github.com/sympy/sympy/wiki/GSoC-2017-Report.
I feel that the number of people expressing interest in participating in GSoC and introducing themselves is somewhat smaller than the number of people who actually apply. After all, you need to satisfy a patch requirement and put a lot of time into thinking through and writing a proposal.
So don't be discouraged, just give it a go. Have a look at the GSoC ideas page and see if anything appeals to you.