The key to not having tests hinder design is to do “spikes”, ie, prototypes you throw away. The most important design factor TDD helps me with is, as you said, boundaries at the integration layers. In any event, I don’t judge the way people do things too much—unless you are on my team 
But there I just want people to be on the same page and it’s chaos when a single team is using different methodologies.
Of course this is an interesting take that I now see @dimitarvp shares. What is the context of this? Like you don’t want people to go on massive pet refactors? You don’t want features too change too often? It’s not a sentiment I’ve thought about before. Oooooops, I totally misread that 
