FICO will specifically look at, per this CC, your change in util, impact to your mix of credit, impact due to the new TL, impact to your AAoA, and of course the history of the CC, which is nonexistent.
You'll get dinged due to the new account (since this is a new Discover your DH got). IME, I've lost 20-25 on avg. Of the 20 or so CCs added, I've found that virtually all of the points have returned within a year, with most coming back by 6 months. I think you'll still have a net ding for that credit aspect come November.
Another thing to think about is the impact to your AAoA. You'd have to do some math on each report to see if your AAoA changes or not. It might not (FICO rounds down and scores off a whole number). If no AAoA change, then don't worry about this. If you lose a year or two or more, then there's a potential for an additional loss that may or may not be recoverable come mortgage app time.
Then comes the util to possibly offset any loss now and/or by then. Again, you'd have to do some math. Ideally and outside of this CC, you really would want to be in the practice to lower util by paying down doebt vs. adding credit or asking for CLIs. Lowing balances will lower your DTI which is apart from FICO.
Finally, an improved mix is a possibility if you are lacking CCs now. That depends on what you have already.
In short, if you have no CCs, AAoA isn't impacted, and /or util drops significantly, you can see a nice gain if added. Worst-case scenario is that you do see a drop, you can always drop as an AU come this fall.
