I would (and might one day) create a script to install the full lightning stack to empower users currently stuck with whatever decisions Umbrel might make because they don't have to technical understanding required were Umbrel big blockers during a blocksize war.

Offline receiving

If I don't have to know how or if it can be done: Predictable fees

PTLCs

Payment channel closing fees should always be paid by the channel closer.

I think the game theory would play out much differently if you had to think long and hard before closing out a channel and paid the fee.

As it stands right now, I can open a channel with anyone and they can just close it and I have to pay the fee.

Never exposing IP addresses.

eltoo now

Make it possible to run a pruned node that lives on your phone and you could establish a channel all from one device

A few sats from all transactions go into my wallet magically.

Improvement, optimization and unification of all the protocols of all the existing wallets between Lightning, not all of them can send payments to each other, you have to work on that

Not the most urgent thing, but since all of the other stuff was already mentioned:

It would be great if you could combine multiple channels into a single bigger payment. Right now the maximum amount one can send at once is the biggest channel's capacity.