I'm currently choosing between two viable software designs/solutions. Solution 1 is easy to implement, but will lock some data in a propriaty format, and will be hard to change later. Solution 2 is hard to implement, but will be a lot easier to change later on. Should I go YAGNI on this or should I incorporate the exit cost in the decision making? Or asked differently, is the exit cost part of the TCO?

I'm thinking of going back to the customer with this to ask wether or not he thinks the exit costs are relevant, but I'd like to know what the community thinks first.

P.S. Is exit cost the correct term?