Hey,
Here my take.
I have a few questions...
Are there too many masternodes? A: No
Is it possible that one day there will be too many? A: I don't think so. The MAX supply in all time should be around 15M, that make a physical limit of around 15,000 Max MasterNodes (see next Answer)
Is it possible to limit the number of masternodes, A: There is a physical limit which is : (total coin supply) 1000 : so 6,655 is the today's limit
and then have a mechanism for allowing a masternode owner to transfer the right to run a masternode to someone else? A: Sure you can, the same way you can "sell" a wallet or privatKey + MatnodePirvate Key (but I don't think it's the best solution as you can't be sure the seller didn't own backup or paper wallet... Best is to sell 1000Dash send them to buyer address and the buyer need to make his MN (about half an hour is enough)
Just thinking ahead.
The way this is supposed to work is that market forces should push coins out of Masternodes, and make them circulate. If they don't circulate, there will be no users and no reason for being, then no reason to hold a masternode. It should become a pressure cycle. I don't think we need to worry about how many Dash are locked up, but rather how many people are using Dash for their transactions. The more people who use Dash, the more coins will be on the liquidity side of things. And the way to get that is to make Dash work, and work well for the users so they'll leave other systems and come to us.
Ultimately, we are a service. The service Dash provides creates value. The value doesn't just come from thin air, it's earned. That's the thing most non-crypto people don't seem to understand. Most cryptos are valuated by their potential to be useful. Most cryptos have not become as useful as the valuation would imply in my opinion. With the road map and past accomplishments of the Dash Team, I actually think Dash is very undervalued. Mostly because the Dash Team understand this principle and are working to become extremely useful and easy to use to every person on the planet. It sends chills down my spine! And yet very few people in this crypto space seems to understand the implications of that. But that's very much OK because it allows Dash to grow organically and allows all of us to see, organize, evaluate, and plan with very few setbacks. (knock on wood)