I commented on the SC issue, but I agree with this.
Treating .abi3.so as the same thing as abi3t is breaking the contract of abi3, and as far as I can tell entirely unneeded since the importlib machinery supports multiple suffixes to look for, and thus the FT build can look for .abi3t.so and the GIL build can look for both .abi3.so and .abi3t.so.
The PEP is already treating these as distinct items in wheel tags, because treating them the same would be horribly backwards incompatible across the entire ecosystem. It’s not any different for treating them the same in the filename except that maybe less (or at least different) people would be impacted.