So we already have the beta welcome dialog, I think we should add something like "Users of slow computers should consider doing this." after the "You can keep using the wikitext editor by clicking the "Edit source" tab instead – unsaved changes will be lost."

The plan is to get rid of the beta welcome dialog relatively soon (in the next few months), however…

Timo thinks we can measure performance and display an edit notice if it's slow.

We discussed how to do this in #mediawiki-visualeditor a bit. Some quotes:

<Krinkle> when a certain amount of time has passed (potentially taking the document complexity in account as well, avoid measuring network by accident), set a boolean flag, which in getEditnotices() will make it include/exclude that notice accordingly
<Krenair> I'm wondering what operation we should measure and what timing shows a reasonable speed
<Krinkle> Krenair: one or more of the actions in the setup of the surface (parsing of html into data DOM, conversion to linenar data model, building of CE etc.)

<Krenair> but those operations will all take different times depending on document length/complexity :/
<Krinkle> Krenair: Yes, but avoiding I mean, taking into account
<Krinkle> e.g. not timespend > maxtime, but something like timespent/doc-size > maxratio
<Krinkle> RoanKattouw might have some math ideas that are more useful
<Krinkle> However, we should probably do some research and see how slow the 'too slow' browsers really are.
<Krinkle> We might be able to measure it with a very simple operation at a small scale (e.g. create an iframe and attach it, just a random unused iframe), that that one operation is measurable enough, we can do it that way.
<Krenair> Hm. This is getting increasingly out of the 'MediaWiki integration' part
<Krinkle> The function calls are all in viewpagetarget in setupSurface
<Krinkle> though ideally this would probably be in ve-core, seems a useful statistis

Roan, could you comment on this when you have time please?

Change 135046 had a related patch set uploaded by Alex Monk:
Attempt to detect slow machines and show an edit notice

https://gerrit.wikimedia.org/r/135046

Change 135046 abandoned by Alex Monk:
Attempt to detect slow machines and show an edit notice

Reason:
This is seemingly impossible for me to get right, and just not worth the effort

https://gerrit.wikimedia.org/r/135046