What if Carlton acquired LWT instead of Granada?

This somewhat confuses me in the series of ITV franchise takeovers following the enforcement of the Broadcasting Act 1990, considering Carlton shared the same transmission facilities as its weekend counterpart at The London Studios, you'd think that, with their pre-established integration, Carlton Communications PLC would have swooped in for LWT Ltd. in late 1993-early 1994, before Granada Group PLC had the opportunity to, especially if it meant a larger commitment to home-grown programming.

I mean, technically they were united with the formation of ITV plc in 2004, but the franchise names had been well defunct on-screen for over fifteen months, aside from mentions in programme credits and production endboards.

Were there still restrictions that prevented the ITV London weekday and ITV London weekend franchises being owned by the same licence holder in the early 90s? That might explain it?

YES, no one could own both weekday and weekend London ITV it would give them to much power.

On a related note, due to competition laws Granada had to sell HTV in 2000 and Carlton bought the station. HTV then ended up with a very unique "best of both worlds" ident package for two and a half years.

More specifically, the broadcasting facilities were sold to Carlton, but Granada held onto some of HTV's programme production assets.

That's not strictly true. Granada retained "United Wildlife" in Bristol which consisted of Partridge Films and Survival. It was run fairly autonomously to HTV West and was integrated within United Productions. It was rebranded Granada Wild and then stripped of anything worthwhile.

Granada came very close to selling half of HTV to Canada's Canwest, which at the time was Granada's partner in TV3. That would make for an interesting "what if"! Other bidders were STV and Channel TV's owners.