I am a cyclist, and have taken my bike by train on the odd occasion.
For anything other than the odd local journey the whole system is quite offputting
- Different ToCs have different rules, so trying to plan a journey involving multiple ToCs becomes a near impossibility
- How do Advance tickets and 'first come first served' work
- If I am travelling late in the day and have to miss a train because the cycle spaces are full then I may miss my last connection home
- In the event of distruption RRB's don't take bikes
- Getting across London is nearly impossible unless you actually cycle between the stations
Given these points its not something I would do.
Rail and cycling should be a good combination, as a bike is a good way to complete the last leg of a journey from the station to your final destination.
I would actually happily pay for a 'bike space' up to a reasonable amount, if the rules were then consistent and better provision was made to address some or most of the problems. Otherwise I can see a situation where bike are not going to be carried.
As with most things railway related the current fragmented system hasn't helped, and the drive to reduce 'wasted' space means rolling stock procurement seems to be in the 'not quite enough' category on a lot of routes since privatisation.