I know this thread is for OP's tl ideas but I don't want to gunk up the site with another small three reply thread and some other people here are doing it.
I have an idea in mind for having Arminius staying loyal to Rome and possibly doing something like becoming a popular senator or even Emperor if I want to be ambitious (will require quite a bit of brainstorming and a weird POD/ butterflies). Obviously it's going to be based heavily on the Rule of Cool where the other rules get fudged a little bit to make things more fun. Thoughts?
Emperor might be a bit ASB, the Senate would had a collective hearth attack with a German foreigner leading the Empire, but senator is possible and there were precedents, Caesar placed gallic chiefs on the Senate if I'm not wrong.
But having Arminius as loyal to Rome would had huge implications.
Now a German revolt against Varus, or other governors, would happen but without Arminius convincing Varus they wouldn't had marched in unknown territory. Maybe it would evolve like the Illyrian Revolt. No massacre of the Legions, no "trauma" and no stopping the expansion into Germania.
I like the idea.
Now for all of you, you can post any TL ideas here, you want as long as they are during the Time Frame of the Roman State.