Things working against a possible Ryder series sequel as of right now

It will depend if Solas makes an appearance or not in the next game, for the moment we are pretty much in the dark except for the setting that will be Tevinter. The rest it's just really our own speculation for the moment.

Why would not being able to seal rifts matter when Solas doesn’t even plan on creating them?

I absolutely do not want the Inquisitor to return like how Hawke did. They completely ruined my Hawke, as well as Revan in SWTOR, and I do not want to see the Inquisitor suffer the same fate. I’d rather they not show up at all than getting the NPC treatment and this ruining my favorite protagonist so far.

Wasn't his arm chopped off, meaning he can't close rifts anymore?

Yes, but wasn't that the impetus for the Inquisitor leading the Inquisition?  In fact, the Inquisition might not even exist (depending on your choice at the end) so to me it would be better to avoid the subject and move on to another protagonist that wasn't part of the Inquisition.

Honestly, I don't see a reason to change the format of DA (new protag in each game) other than an attachment - which people had both to the Warden and Hawke.  (I know I was annoyed that my Warden was gone and replaced by Hawke, but I moved on and enjoyed the new leads.)

No, the mark on your hand made you an important asset to the Inquisition but it is not why you are made the Inquisitor. You are made the Inquisitor due to your own actions, from getting the mages or Templars to join you as well as the leadership you show at Haven as it is attacked. By the time you become the Inquisitor, the Breach doesn't even exist so the whole time you are the Inquisitor you are going after those responsible. 

Also the Inquisition, or at least a new secret Inquisition, always exists after the events of the game with the Inquisitor leading it. We see this both in the final cutscene as well as the Knight Errant comic series that takes place after Trespasser. The choice whether to disband or become part of the Chantry is basically for show, which it even hints at since the decision describes both how much influence you will have and how vulnerable you are to infiltration. No point for the game to say that if you are actually gone for good.

I don't want the Inquisitor to return as the protagonist because I'm attached to them. I want them to return because Trespasser started a new story that involved making the Inquisitor Solas' foil. If DAI ended with the base game where the Inquisitor is looking at the sunrise and then we get the scene with Solas and Flemeth, I would be fine with a new protagonist since that ending is an ending for the Inquisitor's story. However with Trespasser that no longer became the ending of their story but instead the beginning of a new chapter. 

No, I want to change the way DA works because I don't think that story quality should be sacrificed for some unofficial arbitrary rule. You mention Shepard so I will bring up the example I used earlier. If Shepard after defeating Saren or the Collectors and getting involved in the Reaper plot was to just not fight or advise someone new in the actual Reaper War, the story would not be as good as Shepard facing them in the war. However likewise now that the Reapers have been defeated, Shepard's story is concluded because they defeated their enemy thus the protagonist defeated the antagonist. Trespasser made Solas and the Inquisitor antagonists of each other and that plot hasn't been concluded yet. Concluding it with someone new hurts the story on multiple angles. Besides, even Bioware said they would change the formula if they think they needed to for the story. As for the missing arm, what a great way to explain why the Inquisitor is at Level 1 again: they need to relearn everything they knew with a new arm. 

I like how they allowed that with Ryder, where you can toggle between being right-handed or left-handed. 

I liked the scenes, but I think in games it's best to have a few nearly nude shots and implied sex rather than full on cg banging.
That goes for any game. More tasteful shots. Sex in real life is usually goofy anyway if you think too hard about it...