Perhaps you could design a fully waterproof, breathable technical jacket using neck and cuff seals and a drysuit zip. Obviously it would need to have trousers built in too. But then it would be a drysuit!
For "short distance/day tripper" use in good conditions then most decent outdoor clothing will do. If anything more than jeans, fleece and a windproof are needed, then it's a drysuit for me.
I think that most of the "obvious disadvantages" of drysuits are actually "perceived disadvantages". It's not that difficult to get one on and off, and although some people just don't get on with neck seals, if they are properly fitted they aren't uncomfortable.
I haven't looked at prices recently, but I would guess that a Ravenspring drysuit isn't all that much more expensive than a set of top quality waterproofs -- the real "obvious" disadvantage is that a drysuit is less versatile than conventional waterproofs and probably not well suited for hill walking
The big advantage of a drysuit is staying dry. If you can find another solution then you're probably onto a winner!