> Some of us might argue that you have to do that anyway, for any software you write.
Yes, but if your software is another implementation of an existing language, the burden is an order of magnitude smaller because almost all of the existing docs for that language apply to your implementation too.
> On the other hand, the last three points are really not requirements unless you are creating a general purpose language and have a large audience.
Even if you have a small audience, if you want them to be productive, they need good tools and resources. Part of the reason why it's hard for DSLs to be effective is that most of the resources get amortized across all users. When you have a small audience, you can't justify building all these tools and docs, but the users still need them and their productivity suffers in the absence.
If your audience is too small, I think it often just doesn't make sense in terms of cost to make a language for them. You're usually better off using an existing language that already has those resources you can leverage.
Some of us might argue that you have to do that anyway, for any software you write. In fact, a similar argument might apply to your first point.
On the other hand, the last three points are really not requirements unless you are creating a general purpose language and have a large audience.