I wouldn't use software like that. Imagine you build a company using some software, and it was free until you hit $X in revenue. One day far down the road, your company is doing well and you start to get close to $X. You realize you have to acquire a license, ask them for one, and now... you just have to pay whatever they ask for? You're locked in to someone who could quote you whatever price they want. Unless it's really easy to rip out this software, it seems like a huge pain.

I would love that, and think it's a great model (basically "you don't have to pay us if/while you aren't making money from this"), but as far as I understand it, it's hard to enforce. Amazon can just make a subsidiary that makes less than that amount (or no money at all) and skirt that requirement.

Easy to work around with "hollywood accounting". Amazon could license the software from a shell company they own that makes very little revenue.

It would be a much stronger restriction than they're looking for. If no developer at Amazon, Google, etc. is allowed to even use Elasticsearch, that severely impairs the viability of the project. (Depending on the revenue threshold, it could end up being a problem for Elastic too - they're not exactly a small company.)