Forget the disparity between mountain and road bicycles. Their differences are subtle compared to the variety you will see in production recumbent bikes, never mind bespoke experiments. The recumbent community hasn't yet decided if the front wheel should be ahead or behind the pedals, and if handlebars belong above or below the rider. Most drive the rear wheel, but some drive the front. More than 2 wheels aren't uncommon, with most 3 wheeled vehicles putting the pair of wheels at the front.
Some tandems even have the stoker facing backwards.
I started with a commercial long wheelbase recumbent, but since then I have built my own. Curiosity about steering geometry led to Frankenbike. A study was done with a bicycle constructed with an adjustable head tube and fork. The results were published in the proceedings of the second velomobile conference. One surprising choice was essentially the reverse of normal practice.