Yes, liquid injection has some nice properties. You lose the reduction in power completely because a liquid fuel doesn't displace as much air as a vapour.
I understood the tank-mounted pumps caused problems with them, though?
I would imagine it's also not easy to keep the whole fuel supply system liquid either, given underbonnet temperatures?
You could probably drive the injectors from the petrol ECU pretty much directly if the fuel pressure is under decent control and the injectors correctly sized. Gone is the need to compensate for vapour pressure and temperature. I guess it wouldn't need the same enrichments during warmup, though. :-/
Problem is, it's not the cheapest solution, and everyone in the LPG supply chain is interested in supplying "cheapest possible" solutions to people whose only motivation is to save money hence we're only just starting to get away from god-awful mixer systems being the norm.
It's a shame, because I think LPG has potential to offer good performance benefits for those who care to put their hands in their pockets and build something a bit more optimal than a bolt-on kit on a standard engine.
Kevin