Hello TilW.
Would it be possible to upload logs related to this incident? Also can you please describe the reproduction method in greater detail?

With "potentially log the specified addonList" I just meant the message printed in GetGame().PlayGameConfig(), a function which calls RequestScenarioChangeTransition().
It's not actually relevant to the problem other than that it confirms I did not just accidentally give it the wrong input. Apart from that, nothing is logged either way.
But here's some detailed info on how to replicate the problem:

Part A: Verify it works in Singleplayer

1. Open Arma Reforger (standalone game - probably since you're dealing with addons, it won't work when playing from the WB).
2. Open any scenario, like e. g. GM Everon.
3. Either via a console or some previously created mod script, run:

GameStateTransitions.RequestScenarioChangeTransition("{2BBBE828037C6F4B}Missions/22_GM_Arland.conf","58D0FB3206B6F859,5614BBCCBB55ED1C,595F2BF2F44836FB");

I am using 595F2BF2F44836FB (RHS Status Quo) here, but you can obviously use any non-loaded mods GUID.

4. After you ran this, it should switch to Arland and the mod should be enabled.

Part B: Verify it doesn't work on Dedicated Servers

1. As before, start a dedicated server without mods.
2. Run RequestScenarioChangeTransition() on the server, with the same parameters.
3. It should still load the scenario, but the mods will not have changed this time.

Thanks!
Do you know if this will be supported in the future, or not at all?

Unfortunately I cannot provide any further info.