Yes, a better idea is for Britain to get used to paying a lot more taxpayer subsidy for its railways, for one. Another is to stop the culture of over-engineering everything on the railway. Ashley Down is a simple two platform station that cost £73 million. That is insanity.
The idea you'll stop people splitting their tickets by just pricing per mile misses the point entirely; that isn't the problem at all. It's that Britain has so little spare capacity on much of its network - and much of what we have is poorly utilised - that almost none of this thread's premise is worth bothering electrons to put to screen.
There is; there's a lot more availability for Advance fares that way, for a start. There's a huge load of wasted capacity via NMP because of station dwells, destroyed connections and a lack of interest in providing a via NMP fare from many stations - but the latter is a function of ORCATS, the real villain in the room here (hello to the often totally wedged LNR services going via Weedon!).
Mileage based pricing is a deeply unserious proposal for the UK rail network. Capping is almost as bad, because as
@35B says - prices float to the top when they are constrained in this way and you would find a series of unintended consequences if you try it. Should tickets be cheaper and more affordable? Would be nice - but not a priority in the current climate where the service is not good enough. This is just a "I would like my flexible train tickets I use on days out to be cheaper" thread.