Breakfasts? I'm not sure that is actually true. Most components of a traditional full English (i.e. not adding chips, hash browns etc) are entirely reheatable/microwaveable without really detracting from their quality, and if you use a Subway style toaster oven even more so. Heat them up then put on a silver platter and it looks just as good. The only issue is egg, but this can be worked around by providing small omelettes or even Spanish omelettes (which do add the potatoes), as indeed I believe they did on Voyagers which don't have a "proper" kitchen. That just leaves you needing a toaster.
For other meals it doesn't have to be steak and chips, plenty of stuff can be done in a microwave and still give a really good impression when served on a proper plate etc (go into any M&S, Waitrose etc and you'll find plenty in the ready meals aisle). It's about choosing the right meals to offer. DB seem to be reasonably good at this for the Bistrowagen.
I don't think you can offer anything really approaching a proper British fry-up without the use of a frying pan. You can do a rather pallid impression of half the ingredients, but the rest of it just isn't worth trying. Far better to accept that there are other things which can be eaten for breakfast and concentrate on the ones you can do in a microwave/combi oven, George Foreman or sandwich press.
The microwave operations on Swedish railways are pretty impressive, with substantial lines of people from across the train appearing at certain times of day to pick out a meal from the well-stuffed fridges and microwave it in one of the multiple self-serve microwaves. In terms of real food, the most successful stuff tends to be the part-cooked stuff as well - pierogi in Poland which takes 3 minutes in the already-boiling pan of water, crepes which get a minute in a frying pan (or microwave at a push) and some cream sprayed over the top, schnitzels that are part cooked and fry in 3 minutes.
Basically you can turn round a lot of covers in a short time in even a tiny kitchen, and if you have a reasonable supply-chain and the willingness to give 2 seats of space over to storage, you can offer a decent range of different food at the temperature it should be. What is offered on UK trains is a long way from state of the art. If anything an unreasonable level of pride in being able to knock up a mediocre fry-up is holding us back.