To merge, or not to merge?

I'm wondering whether to include the ability to merge companies in the later phases of the game. Historically, the major companies did not merge until they were grouped into the Big Four in 1923. But some of them did work together, for example to run trains along the length of the East Coast and West Coast Main Lines. So a game merger would not represent a literal reformation of the companies, but would reflect growing co-operation between the companies.

My reason for contemplating this change to the design is that I'm still worried about managing the number of companies. If they each have to own a permanent train, that will be a lot of time spent calculating income. It could undo the benefits that I hope to gain from a simpler income mechanism.

It might also have a desirable side-effect in reducing the number of company markers that might be in play. This in turn would let me simplify the tile upgrade paths in some cases. This is not a major consideration, just a "might be nice" outcome.

If I adopted this approach, I would allow companies to merge once the brown tiles are available. Two five-share companies would merge to form a ten-share company. A ten-share company could merge with another company by swapping shares on a two-for-one basis, as in 1841.

An alternative might be for me to combine some companies at the outset. For example, I could decree that the GNR and NER would be represented by a single company in the game. Possibly the LYR and the MSLR could be similarly combined for game purposes. Or the LYR could be combined with the Caledonian, the NER with the NBR, and the MSLR with the Midland.

These are just musings at present. More testing is needed!