there’s nothing about software development that requires meatspace interactions
This is a big claim that is not true in my experience. Dealing with highly ambiguous situations, talking people out of bad ideas and learning through collaboration works much better in person.
I'd imagine it would be very hard to switch to that kind of model after all this time. Wouldn't guaranteeing a permanent level of support would likely involve hiring people and having to bring in enough to support them too?
It might not be that hard if you're motivated and have that vision, but I can completely understand someone not wanting the added pressure after all this time.
The performance of a "for loop" is usually dog slow (some special cases were optimized recently). You often spend hours figuring out how to vectorize your code so it runs decently fast.
A similar story for Python and NumPy on this point, mitigated by NumPy's elegant broadcasting rules. Agree with everything else!
Basically, what @okey said. Your company looks really cool, but financial security is a much stronger motivator for most people in the long term.
Look at what other people are offering in this thread, on Glassdoor, on angel.co and similar. I've never heard of a developer being paid £20k in London and I'd worry about working at a place that hired people at that rate.
You might be able to get someone fresh out of undergrad for £25k for your front-end role, but not a developer with proven skills. You might find a developer wanting to try out your lead role for £55-65k, but not someone who's already shown they can perform that role successfully.
Maybe you will get lucky and find the right people, but it's a gamble and any good people you find will probably not stay long. Anyway, I wish you luck despite my naysaying.
Bear in mind the kind of people you want to hire for a lead engineer role are unlikely to apply in the first place, on the off-chance that you'll make them an offer significantly above the advertised range.
Anyway, best of luck - anything to improve the rental situation in London is very welcome!