I worked at a couple of dev tool startups that required you to invest some effort to adopt and would require effort to move away from (e.g. if the company went under) - open sourcing ended up being basically a necessity to sell the product (enterprise sales during seed and A). YMMV, but I would definitely encourage open sourcing enough to make potential adopters feel comfortable that they won't have to do a big, urgent migration and/or lose a bunch of engineering investment if you go under or decide to pivot.