I miss when custom ROMs were easier. Practically every phone with Windows Mobile supported custom ROMs. I tried a lot of custom Windows Mobile 5.0, 6.0 and 6.5 ROMs back in the day. It was pretty straightforward on older Android, too.
These days, it seems like so many phones are locked down, for example with a locked bootloader. It's so dumb. If I paid for my phone, I should be able to do whatever I want with it. Why even some tech-savvy people are comfortable with being limited in terms of what they can do with their expensive devices, I'll never know.