From all the S-1s I have read, this seems like a typical disclaimer. More than anything is a guidance on the use of OSS and the risk that comes from using non-propietary technology (which includes releasing software written on top of the questioned technology). The way I see it, it's more of an indication on potential future litigation (e.g: Google vs Oracle), not so much of the cost of re-writing software, although I'm sure this is included because it seems like the reasonable thing to do if you're using software with a license that is potentially harmful to your business' economic interests.

This is why companies care about OSS licenses and sudden changes in those licenses. It's not out of pettiness. Automattic dropped React just for this very reason.