A lot of the special chips don't present the signals needed on the cartridge connector, so that won't work in many cases. This kind of thing is mostly used to work around the CIC chip, but it's been cloned so that's not necessary anymore.
As far as I can tell, all of the functionality of the old T-Connectors has been built in to these carts. The tototek snes t-connector was only able to handle the DSP-1 chip, which the SNES EverDrive Ultimate now has built in. The T-Connector for the old N64 copiers was basically just for the CIC to switch between the 6102-6106 chips. All of that logic has been built into both of the new N64 flash cards.
I agree that it would be awesome if there was a T-Connector for the SA-1 or Super FX chip, but I'm afraid we may be out of luck. The save game part might be doable, but I'm not sure it would be worthwhile for Krikzz to make. Here's hoping:)