I don't think anyone has seriously considered it, when you can go TPI or TBI for under $1000 finished.
The custom setups IMO still aren't worth as much as a stock one, typically sensors are removed, and the system is simplified enough so that it will still run, which is all many "hot rodders" want. Removing functionality of a stock system is removing driveability, which is one of the reasons an EFI swap should even be contemplated.
I'm one of the "do it right, the first time" kind of people, and GM did it right, none of the companies out there are qualified to second guess all the time and money spent by GM on their EFI systems. (I know about Howell, but I'm generalizing here) Many of the aftermarket systems are just poor/less functional copies of stock systems.
The trucks aren't hard to put this stuff in, comparatively, so looking at ways to change the stock setup really isn't practical. Whats wrong with the TPI or TBI intakes for a fairly mild motor? Nothing. Why would you want to have to work with mismatched components when you could just go into a store and say it's an '88 Camaro (for instance) that you need a TPS, or MAT, or O2, and so on, for.
Once you start talking about a high revving, or large CID engine, the stock TPI (for instance) starts to show it's weaknesses. But for another $1000 or so, you can get a setup that eliminates the long runners, with no "hassle".
Retrofitting multiport to a dual plane carbed intake is pretty pointless, the long sweeping bends (or complete lack of bends) is what you want in a multiport injection setup, TBI needs the dual plane because of the air/fuel mix. Most of the time when you see carbed intakes being retrofittd or considered, is because someone is dealing with Olds or Pontiac engine (again, those used for example) that were never outfitted with a modern fuel injection system, and thus, have no easy way to go with EFI, like what exists for both BBC and SBC.
