We have the possibility now to replace Textbox.io editor with TinyMCE. I like this new addition to the product and I did not have any issues with.
Replacing the old editor is really easy, basically you use the same process as updating Textbox.io.
But do take care, some formatting, in Wikis for example, will get lost after you switch the editors. So make sure to fill your test environment with some articles from the production and check with your users if this poses a problem for them.