I got it. I was trying to explain that it’s getting hot because the app is doing a lot of work (even if partially due to coding inefficiencies). More RAM won’t make it run any cooler or last longer on battery. In fact the opposite is true to the extent that more RAM would help performance.
Hard to predict, but I would not expect much change until the last supported OS, which whether by design or inevitability tends to run less well.
The bigger issue is that web browsing is no longer a light activity but often the most demanding work home computers see. YouTube now has 8K video streaming. Web apps span the gamut from light to very demanding of CPU, GPU, and memory. I would expect that to get worse over the next five years. Doesn’t mean an 8 GB machine would become unusable but perhaps a little compromised: for example, requiring the user to close other apps and unused browser tabs (which are good decluttering habits anyway, in my opinion).