Jimbob: "If [RM] truly is [streaky] then a positive progression would work well IF you had some way of determining when the streakiness is going to be in your favor."
I'm not sure what you mean by "streakiness is going to be in your favor." Even though I'm not a statistician by trade, I'd like an explanation in more precise (perhaps mathematical) terms. For instance, perhaps you mean to say that we need to determine when a hand(s) has positive expectation. If so, then a positive progression would indeed work, but guess what would work even better ...
You want a hint? OK, your hint is ... flatbet.
You got it--the answer is to flatbet the max on the RM on any positive-expectation hand. Despite the "streakiness"--which might be a layman's term meaning, "You can lose lots of hands in a row and get crushed"--are we really worried, when the table max on RM is usually a paltry $25 (and never more than $100)?
jimbob: "What kind of shuffle is used at the places where you play this? Perhaps the shuffle could explain the streakiness."
Scapegoating the shuffle is second only to scapegoating the RNG as an explanation (always a bad one) for any and all phenomena that are not understood by the baffled rookies (who are usually losing). The shuffle has nothing to do with this. Do you know the probability of winning a Royal Match bet? Whenever the win probability of an event is low, it feels "streaky" to the layman. That is, they lose LOTS of hands in a row. Then "suddenly" they hit two or three winners. Wow, it's "streaky"! Indeed.
I strongly advise anyone who has the capability of doing Royal Match analysis to not waste their time. The Royal Match bet has no practical value, and there are other side bets out there that are worth much more, and easier to count. Arnold Snyder has already done an analysis of Royal Match in his "The Big Book of Blackjack."