To clarify: this already works when you do things like https://en.wikipedia.org/wiki/Special:Recentchanges?days=23&limit=42 , it just doesn't work when you do the same thing through your preferences.

@Catrope - the selector will display custom numbers if they are in url, but the user settings do not get to url - could it be a (slightly or entirely) different problem?

Right now user settings for days/number of changes are not properly preserved:
in betalabs:

• set a custom limits on the number of changes displayed and the days
• click on the 'Recent changes' link in the right navigation menu: RC is displayed correctly in terms of UI displays (the number of records and the days). Notice: The url displays the system default settings though, not the user preferences: https://en.wikipedia.beta.wmflabs.org/wiki/Special:RecentChanges?hidebots=1&hidecategorization=1&hideWikibase=1&limit=50&days=7&urlversion=2
• navigate away from the RC page - click back browser button - RC page will be displayed with the system defaults limit=50&days=7
• navigate away again and click on the 'Recent changes' link - RC page will be displayed with the user's defaults for the numbers of changes and days (the url displays limit=50&days=7 still)
• reload the page - the system defaults are displayed on RC

@Catrope
In betalabs "Days to show..." can be changed via RC user preference settings and the changed number will be displayed on RC page;
"Number of edits..." cannot be changed via RC user preference settings - the custom setting can be saved on the Preferences-RC but won't be displayed on RC page.

This is an annoying "feature" of the fact that the original preference updates everything that has lists of pages in it even though it claims to only update RecentChanges.

Opened a separate ticket here: T172156: Make limit sticky adhere to preference limit value

And I have a proposed solution in gerrit.

Change 368949 had a related patch set uploaded (by Mooeypoo; owner: Mooeypoo):
[mediawiki/core@master] [propose] RCFilters: Use the base default for 'rclimit'

https://gerrit.wikimedia.org/r/368949

Change 368949 abandoned by Catrope:
[propose] RCFilters: Use the base default for 'rclimit'

https://gerrit.wikimedia.org/r/368949

This should be fixed; see T172156: Make limit sticky adhere to preference limit value

This is fixed - checked in betalabs and testwiki (wmf.12) - user set Preferences-RC for 'Days to show...' and 'Number of changes...' will be displayed RC page filter day/change selectors.

QA Recommendation: Resolve