There are currently 23 QBs in the HoF. Of that 23, there are 8 whose career primarily started/was in the 80s or later. The five locks from the 90s+ are Manning, Brady, Favre, Brees, Rodgers. I think Warner should be a lock, but that's another discussion. He'll get in eventually, just not on the 1st ballot. Roethlisberger likely gets in due to his Super Bowls.
So that's 7 that are going to get in before Rivers. It's likely going to be 10-12 years before all of those guys get in before he's even seriously considered. And by the time he's seriously considered he gets lumped in with the Drew Bledsoes of the world. Plus Eli and his 2 Super Bowl rings is out there. Then a couple more years and younger guys like Stafford and Ryan become eligible and they have another decade to improve their standing. And if he's not in by then, well guys like Luck, Wilson and Newton will start becoming eligible.
For a solid decade of HoF voting he won't be the #1 QB on the board and he'll be competing with all the big names at other positions. Philip Rivers or DeMarcus Ware? Phillip Rivers or Julius Peppers? I mention that last part because we know the HoF committee likes to limit how many people they induct each year, no matter how stacked the card is.
You are stretching to make your case IMO, and you don't really have to do it. I'm pretty sure no one has posted in this thread for years who stated that Rivers is likely to make it. As to your post here:
1. In the 1981-1990 HOF classes, 8 QBs were inducted. Then there was a lull in the 1990s, with just 2 QBs inducted from 1991-1999, one of them Jim Finks, who played in the 1950s. Then in the 2000-2006 HOF classes, 7 QBs were inducted. There have been none inducted since, partly because with the rule changes, improved training/medicine, etc., elite QBs are playing longer careers. But this shows that QBs have been inducted in bursts. And now we are in what amounts to the golden age of QB play. So it is possible that a high number of peers will be inducted.
2. Favre is a lock and will be in on the first ballot in the class of 2016. Rivers probably won't be eligible for another 8+ years after that class, so that has no bearing on his case.
3. In part due to the lull referenced above, I expect Warner to make it NLT the class of 2018. Still well before Rivers becomes eligible, so not really much of a factor.
4. If Peyton retires after this season, he will be a first ballot lock in the class of 2021. Still likely 2+ years before Rivers becomes eligible, so not really much of a factor.
5. It seems that Brady and Brees both intend to play at least a few more seasons, barring major injury. So their timing could be similar to Rivers or he could trail them by a few years, depending on how long he plays. Regardless, both are obviously first ballot HOF locks.
6. Rivers will likely be eligible for at least 5 years before Rodgers is eligible, so he may not affect Rivers' case. And all of the other younger guys you mentioned are irrelevant to his case because they will come much later.
7. So when Rivers becomes eligible, it will probably be true that in the preceding 18-20 years, 5 QBs have been inducted (Favre, Warner, Peyton, Brady, Brees). With another lock on the medium term horizon (Rodgers, 5+ years away from eligibility) and perhaps by then another lock or two (Luck? Wilson?) on the longer term horizon. I don't really see the big problem you are saying exists with the number of competitors who we know now will very clearly be ahead of Rivers.
8. This will leave Rivers competing with Roethlisberger, Eli, and perhaps Romo. All of them still have years to play, so what they accomplish from here forward will determine how they compare in the end.
9. Romo is by far the least accomplished of the group of peers mentioned, and he turns 35 in less than a month, so he is also the oldest and thus likely has the least amount of time remaining. I think he has no shot, unless he finishes very strong, including at least one Super Bowl win.
10. Roethlisberger and Eli would have a better chance than Rivers today, thanks to their championship rings and because both of them play for historically popular east coast franchises. But IMO Rivers has clearly been a better passer than both of them, which counts for something. As I posted earlier, if Rivers finishes strong and leads the Chargers to a Super Bowl win, I think he will be in, regardless of what happens with the other two. If he doesn't, he probably won't make it.
11. As for comparing Rivers to Bledsoe, you are making yourself look foolish. Rivers is much better than Bledsoe was, and it's not close.