okay, I ended up having to refund my money for the sram, since it never arrived, but I was able to instead buy 128k worth of sram in a lot of 4 separate 32K chips for the same price, im using two of them one for normal program/data ram to extend from the 128bytes, which the atmega8515 will act as a mmu to read from and write to ram using the upper address bits to access either the mmu or the the dual port ram (IDT7130SA55) which would act as a memory buffer, though i am considering using atmega644 instead of an 8515 for its extra memory, only difference is no port E and but much more memory versus the 8515, but the 6502 would write to the ram, which the atmega would either do nothing, store it, or load it and do some processing, and store back to the dual port ram or store in in its own 32k for later use or vice versa. also i would use the atmega to control the tia and 6502, using the 6502 itself, i.e having the 6502 trigger the atmega which would halt the 6502 using its rdy line, and assume control of the tia, thing is either you can use the 6502 for addressing the tia, but would be limited to the 1.19 mhz clock (both atmega chips will run @ 21.47727MHZ) , or  instead use atmega to handle the tia bus, but the way i would implement this i think most likely would break normal 2600 compatibility unfortunately.

TL;DR

i had reorder sram but got a better deal , i've gotten some dual port ram, current progress is getting the memory map structured properly so that if you plug in a 2600 cart it will run just fine, but you insert a cartridge with homebrew code that would read and write to the extra address space, then you can use the extra hardware added to the system and use the 32k of ram and the dual port ram which the display co-processor would sit behind with its own 32k of video or  just general purpose ram (ie you could store graphics or program data or both if you wanted to).