They are a good choice in some circumstances. Yep right now elec is 3x gas, but that can easily change. Part of the issue (they say they will address) is the tie of elec prices to gas prices which overinflates the price of elec.
Right now and since around xmas the wind has been doing the heavy lifting, gas far less, thats only going to get more and more significant as we get more and more wind generation and more and more solar. The issue is really how we deal with the troughs, hence the talks of storage.
You are going to have your boiler for a while yet.
There are other techs as well. Eg the hot sand storage for use for hot water, so you can use solar and top up from the grid for that. TBH my hot water tank (megaflow) loses around 2kwh of heat a day. The latest will be even better plus its mains pressure, its far superior to any combi I have ever seen
There is of course the ability to have elec showers, so 12kwh for example.
I don't think most boilers use 30kw for water either, I thought it was lower, the higher rating being for the closed loop for the heating in effect.
Its coming, its just a matter of when. Various techs will evolve so picking the best will be key.