It's pretty well documented that you prefer (and find more likely/realistic) the Celtics continue towards the future without Rondo, but this is a little silly.
1) It is not imperative that the lineup "mixes" because we are not going to win a championship this year (which is why you want to trade Rondo in the first place).
2) I have no rebuttal that Rondo's age doesn't work out as the roster is currently constructed, but trading him for pennies on the dollar is not the best option. However, with the way medicine is these days I would not be surprised if Rondo comes back as good as ever. Yes, time will tell, but I think that either way, Smart could use Rondo's tutelage as a big advantage in early development. The rest comes down to opinion and assumptions, but I say let Rondo play and then make a more defined path. Worse comes to worse as you predict and Rondo isn't his old self, we could always let him walk and have some nice cap space. I personally am not a big believer in Mclemore, but to each his own.
3) The opposite could also be argued. If Rondo plays even like he did last year (low efficiency, still great playmaking, mediocre defense) and Mclemore does likewise, Rondo is clearly the better option statistically (situationally maybe not, for example in another rebuild, but that is irrelevant). If Rondo plays better than last year, his value could go way up from where it currently presides, which is the argument you are using to support Mclemore. Of course, the likelihood of both could be debated, but that once again comes down to assumptions or opinion.
The rest of the points are laden with assumptions such as, "what if, in my opinion, probably, and must of."
I respect your opinion as to Rondo, and your opinion about trading him may end up correct (seeming a little more likely each day). I will not irrationally defend Rondo, but this particular post is making something out of nothing (or, more specifically, a twitter post by some guy with a spotty record).
Mclemore had a decent rookie season. He is still so young. He was considered a top three pick for the last draft until the cavs surprised the league by taking Bennett. Danny liked Mclemore but couldn't move up to get him
I respect that stance on Mclemore. I do see how he could be appealing based on flashes he had in college and even briefly in the NBA. However, he was, statistically, pretty bad on a bad team. I think of being an NBA GM to a game of gin (card game-like gin rummy, but with your hand hidden). When making a move, you must consider the upside, the downside, and the likelihood of either occurring. Even when you make the right move, you could end up waiting for a long time, or even lose, simply because you could not predict luck and what others are doing. If you get antsy waiting for the specific card, you may get antsy. Will being antsy get you the win a few times? Yeah. Is it statistically right? No.
If you look at this trade from that perspective (in which you are emphasizing Mclemore), there are a lot of things to look at. The upside of your situation is that the Kings win the lottery (or get a top 3 pick), which would entail not making the playoffs (likely) by a long shot (not too likely to be worse than #5 like they were this year). Now, the proposed lottery odd changes would help your case, which is something to consider. However, it is not a dramatic change. The other upside is that Mclemore becomes a future star, rebounding from a pretty poor rookie season (not likely by any stretch). The median upside is that Mclemore becomes starter-caliber at SG, which is more likely, but we have AB as a decent young starter on a decent deal. Now, a preferred "decent young starter" is up to opinion, as Mclemore would presumably be more offensively-oriented than AB with better size but not as good defense. However, now comes the worse case. The Kings make the playoffs (not super-likely, but more likely with Rondo, as Stauskas could slide into the SG spot), and Mclemore is a bust (once again, not super-likely, but if you look at the "what if the guys remain the same as last year" argument, Mclemore is in trouble). Now, neither Rondo nor Mclemore is likely to perform as poorly as last year, but it is the worst case to consider. If Mclemore is a bust, we are basically stuck with Marshon Brooks on a contract. However, Mclemore performing as poorly as last year is just as likely as him performing like a future star, so the "starter" upside is what is to be examined, and it is a wash with our current roster. The draft picks would be nice with the subsequent direction our team would be taking (probably tanking), but nothing super special, as they are more than likely somewhere in the 5-9 range. If the Kings make the playoffs, we are left with some mediocre draft picks (although Danny is pretty darn good in that range, but I don't like to bank on that).
Now let's look if we keep Rondo. The worst case is that he plays awfully, which would help our tank effort. We may not find a trade partner, but we would get a better draft pick. We could then let Rondo walk with nothing left on the books. Best case is that we get superstar Rondo every night and start a great upward trajectory. Both are not super likely, but the downside is minimized. Median result is that Rondo plays slightly better than last year ("back to old form", perhaps with a lost step, but increased efficiency) which would raise his trade value anyway.
In conclusion: Could Rondo for Mclemore end up better for us? Yes. Is it more likely to help us more than keeping Rondo in this situation? No.