I don't agree with this idea\OP suggestion. Scripting provides mIRC with additional features not included, or possible, by regular design. "Modulular" if you will. Just like any other modular piece of software, e.g. Microsoft Office products, not every feature is included right into the product itself, but rather as add-ons. Scripts are add-ons for mIRC, and dime a dozen.
To take the view of the average user and say the possibilities of functions or features only currently available by scripting is out of the scope for the average user, is failing to see the average user is already very resourceful and accustomed to seeking out add-ons to their software.
To completely satisfy everyone, the internal theme support would need be able to supercede the community efforts behind MTS, in my opinion. Not format-wise (read: not the standard itself <-- for those that take things out of context, *wink wink*), but the issues addressed and developed around.
I would much rather see mIRC move forward to a more plugin based platform, and modularize features, existing & future. Even if it wasn't an open system for all, just "official plugins" released by Khaled that extended the feature base to mIRC. DLLs were a great step towards this dream, but I think further strides could be made that push mIRC (and the community) to a more accessible state for all users alike and secure it's future.