That is an interesting mount. I'm a sucker for original / interesting stuff so I'll get one of those!
My first thought is watch for your knees hitting it when you stand up.
If I was mounting there I would go for lightweight as possible so definitely no AAs.
If you only need a 'be-seen' light, then a small rechargeable would be fine. There are loads of options nowadays for not much money or many grammes.
If you need a see-with light I would go for something with a separate battery pack to reduce weight as much as possible - although wire from that location to a battery is a potential hazard to be aware of (too loose and getting in front wheel, too tight and snagging leading to loss of steering, etc). Thinking about it, a bar bag would be the safest place for a battery as it would also move with the steering so could be pulled quite tight).
An eBay Cree XML battery pack light like this would work well:
https://www.aliexpress.com/item/32614646189.html?spm=a2g0s.9042311.0.0.51f04c4dMR73BDI use a 5v USB version of this with a power bank, and a fresnel lens for an on-road beam pattern. It's my best light.
E-bike lights do work with battery packs. The voltage varies: B+M need more than 5V but the RFR ones work fine with a power bank (I have two of them which I don't really use as not quite as good as the eBay ones for my needs).