As this is quite a long list, wouldn't it be better to switch to a text logo by default (when sitename !== 'Wikipedia'), and then add SVG versions incrementally?

If only this

when sitename !== 'Wikipedia'

is technically possible. that was intended design.

if anyone can achieve that.. let's do it. I want to keep the status quo of "more wikis with correct logo than incorrect one"

Here's early analysis of wordmarks and projects
https://docs.google.com/spreadsheets/d/1JXMMtlSrqbNb6YPKreaQ8zgRqKhaUruJwP5iXYSWG80/edit#gid=1464088164

We have more than 250 wikis with ~170 wikis have the correct "Wikipedia" wordmark. I would want to avoid showing text string instead of wordmark for 170+ wikis.

this helps more wikis than it breaks

On a quantitative basis, yes. But qualitatively the improvement is purely cosmetic (plain text -> SVG), whereas the downside for non-Latin wikis in particular is that have a logo in a script the users might not be able to read at all.

What is the config setting to use plain text?

@Esanders I don't want to have a fallback of plain text which has such small shelf life.

I have prioritized the work of creating wordmarks for all wikis here - https://phabricator.wikimedia.org/T142426
Pending: updating task description with status and tracking

designers will be splitting the work and doing this over next couple of weeks.

Furthermore, is qualitative better here than quantitative is reading web product manager's decision cc @ovasileva
Let's follow reading web process here

Furthermore, is qualitative better here than quantitative is reading web product manager's decision cc @ovasileva

Absolutely! Just sharing my opinion. Having localised SVGs is the ideal solution.