Those teams can join F1 only if every team will have stock parts but in that case, Ferrari and Mercedes will probably leave and found a new circus.
Ferrari and Mercedes will never run with another team engine.
Less good tires are terrible solution and no real racer will ever say different. Point of Formula 1 is to see best racing drivers in the world drive fastest and best racing cars in the world, but not just drive them. The key is to drive them on the limit.
With tires less good as you say we will never again watch cars and drivers on the limit and finding that limit. For me that is the core of F1. Everything else is politics and bullshit for the show which we are experiencing for the last decade or so.
Well F1 has been through some shit show for the last decade that's right. And we, as the fans of the sport, are the ones mildly suffering as it's really shitty to see that the cars aren't really pushed to their limits unlike the heydays of F1 in the 80s to 90s. A lot of the regulations imposed by the FIA on the sport slowly killed the thrill of it. I believe that we can still see the best of these beasts of cars AND still abiding by the rules and safety regulations. However some people within the management--and also some within the teams--didn't have the balls to ask for more power for the cars but instead ask to nerf some of the best cars' best assets in order to play in a level playing field.
Imagine ingenious engineering techniques being added again to some of these cars like in the 80s and 90s and actually having some safety measures being observed. This could have been the best era for F1 with all the tech and all the new stuff we have for automobiles but here we are, teams constantly shouting to nerf other team's cars just because theirs weren't good enough.
If pit stops are designed to not expose the fuel tanks to heat or any other factors that could cause a fire, then refueling can still be possible. Add to that the car's gas tank being exposed already to intense heat from driving at insane speeds. There are a lot of factors accompanied to refueling that the FIA deemed it unsafe--or they are just not really wanting to spare some more money into development of such tech, both the teams and the management.