Semi-hollow oak works for Brian May.
There definitely are many plentiful woods that can be used instead of ash (or any other wood). There really is very little reason to religiously stick to the small handful of woods that were used in the 50s. You can swap most species of ash for pine and, as far as a guitar is concerned, not tell any difference. Alder is considered a 'junk' wood here in the UK outside of the guitar world and can be replaced by half the species we have in our backyards.
Our common willow trees here are absolutely superb for guitars, both electric and acoustic. The grain is like a hybrid of swamp ash and oak (
HERE is an image of what
cheap willow looks like), but as pale as rock maple so you can dye or paint it any colours you like without worrying about the hue being influenced by the wood's colour. It's even possible to get flame-figured pieces; yup, flame on ash-like grain. It's lighter than swamp ash on average, generally around the weight of (decent) basswood. It's about as hard as 'northern' or 'baseball bat' ash, and in fact is the original wood used for cricket bats. Tonally it is also similar to northern ash but with a tiny touch more low-end resonance. Kind of like if you took swamp ash and turned both its high and low extremes up one notch, without changing the mids. It's used by several UK companies for electro-acoustics since its tone comes out totally balanced when hollow.
The only drawback is it's so tough, much like walnut it can be a bit of a pain to cut and shape.
I'm also hearing great things about bamboo. Certainly a sustainable source, very strong and very light weight, but I expect most people would only want it with solid colour finishes and I wouldn't want to guess what the tone is like as I've yet to play one myself, just heard someone playing a hollow one.