When going through your savegames can you remember the techlevel of each planet? I cannot.
After installing or altering an oxp/oxz i tend to go to different savegames to view any changes or go back to an earlier situation.
I would like some more information.
No, I don't remember that particular information. On the other hand I have bunch of save games that I use/need for OXP testing/developing. I have named them so that I know which one is which. I don't mean to judge you or anything, I'm just curious what's your reasoning for this kind of addition. It's not a big or dramatic change, but it's a core change and as such I think it's important to reason a bit about it. Would it be beneficial for all or even most of the users?
I don't need to see the TL on savegames and I don't remember ever needing, but that does not mean it would not be important to someone. If it's important to you, you need to convince the devs it's worth implementing.