Sorry for late response.
1)full VRF - So since we are a service provider we need to create something close to 8k plus vrf instances. VRF lite creates a subinterface for every bgp session peer. But with VRF lite u don't necessarily need to do it like that.
This is not BIRD's problem -- BIRD uses what kernel provides.
2)BGP Sessions- We need scale of upto 8k bgp sessions. That's one bgp session per vrf. Do you think the product currently supports that kind of scale? Or is there a future development cost attached to it?
This amount of BGP sessions should be safe in BIRD itself. Anyway, you may need to increase the filedescriptor limit to allow this number of sockets. I also recommend to set sane timeout values in BGP, not too short. Also, if you have many routes, there may be performance bottleneck in filter processing. Keep in mind that BIRD is still (almost completely) single-threaded and it won't change in near future. (It's quite a lot of work and much more testing.) M.