How about how the R came in so much lower? There are two sides to this pricing guessing game. I do not imagine it getting into the >$3999 region. $3299 is my guess as well.
I think the R came in lower because it was missing a number of key features available on more advanced bodies. Comparing the 5D IV and the R directly makes a good case for this. 5D IV was $3500 where the R was $2300. The 5D IV launched that same sensor almost 2 years earlier, came with two card slots, had more advanced weather sealing and robust constriction, a joystick, better battery life, a faster burst speed when using auto focus, and I'd argue quicker access to controls with more functions having dedicated buttons on the 5D IV.
Even on release of the R there was still good reason to choose the near 2 year old 5DIV first. Considering the rumoured R5 seems to more than bridge the gap between the R and the 5DIV - long surpassing the 5D IV, and arguably the 5DsR, and even in some respects the 1DXIII, I think this could reasonably come with some sticker shock. The Sony a9II launched at $4500, and if the specs are true, the R5 may make a convincing case as a superior sports camera - equivalent burst rates in electronic mode, and faster burst rates in mechanical, with substantially more resolution, likely a better grip, and I'll bet on Canon's weather sealing first too (though, it's all hypothetical until the R5 is announced)
You're right though, it's all a guessing game. I still think the R was (and still is) a pretty incredible deal for the price. When I bought my 5DIV, I was choosing between that and a 6DII - if the 6DII had a price bump and the 5DIV sensor, I would have probably picked that up instead, and frankly I think the R fits that niche pretty well right now.