Thanks for your detailed feedback guys!
The TIO list was limited originally as a hack, because we didn't have paging on the app. This meant that it would otherwise always load all threads you'd ever posted on, which would be super-slow, and heck, maybe even potentially crash a server or two.
The modern way of accessing a big list, is to use the 'infinite scroll paging', which we've now implemented in every thread list in the app. Meaning you can see old TIO if you really want, but they won't be loaded unless you scroll down.
For many of our new users, it's very disorientating to have an unwritten rule where TIO will randomly disappear, when other apps/forums/social networks will always allow you to see a list of every post or thread you've ever made. Consistency with 'what a new user expects' is an important part of the product development process.
Adding a setting to limit TIO, is unfortunately going to be too awkward to fit in the app, since simplicity is really essential. However I appreciate it's irritating when old threads are pushed to the top because of new posts.
So, would this feature be helpful?
The option to order TIO threads by 'most recently active' (default) or by 'how recently I last posted'
If enough Mumsnetters would find it helpful, I'll get working on it.