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Yes, but look how long people coped with home made dual levers. Many people still use home made/rik specials. As I said, I wouldn't be that difficult to make a dual lever. You're probably right that there probably isn't going to be a dual hyd lever as there isn't a demand for them.

Avid BB7's are £60 per caliper
Shimano Deore are £30 per caliper

Paul Levers are £60! £60 for a fucking brake lever!
Shimano SLX are £25 a lever.

The way I'm thinking you'd run 2 master cylinders alongside each other and a single lever. That's still only £50. You'd have to modify it but still it shouldn't be too difficult. On the other hald you could look into some motorbike trials brakes to see the size of the pistons to run a simple t-piece to split front/back.

Please correct me if I'm wrong, but in the 90s Hope made a twin front disc setup with Pace. Swear I remember seeing pics of it in the bike mags of the time for DH racing. It ran from one pretty normal looking sport lever to two twin piston calipers (XC2 calipers?).

Really if you do your maths/ get your micro-calipers out, you don't need two masters at all. Just one lever, but a larger volume job, say that of the monster Mono6 caliper from a few years ago, and then two mono-mini/mono-moto calipers use that hydro 360 headset thing, then make something so you can attach the two frame side hoses fit to the one out let from the hydro headset. Balancing might be interesting, but TBH there will probably be something ideal in the RS catalogue (almost always is) for flow/pressure reduction, or even a decently controlled bleed session would be fine for the most part.
with that ^^^^ you might be lucky and be able to do it with all off the shelf parts for not a lot of money (£120? with used calipers/lever, new headset thing, and clarks braided hoses).

Talking of trashing hoses, I've been riding hydro discs on all my MTB's for 12yrs+ and I've NEVER bust a hose (and I used to crash plenty), I only use what they come with (mostly Hopes, had one set of hayes and two sets of shimanos, shimano had the poorest quality hose/hydro fittings by far).