My first thought of Astros to NL West and let's say the D'Backs to AL West is simpler and easier than all of that, but if you do want to complicate things, I'll offer up an extended scenario that could be completely exciting. Starting, of course, with the aforementioned 2 moves.
Ladies and Gents, I offer up a new MLB Wild Card and Super Seventh Division. Ah, the Wild Card race, such big topic of debate each and every year, and rightly so, as it offers such a unique aspect to the playoffs. The concept of the Wild Card now is that the team with the best record in each league that is not a division leader at the end of the season becomes the Wild Card team. A variation of that should should stay put, but not as the Wild Card, but as the MLB Super Seventh Division. Why the name change? Because, let's face it, often times this team has a better record than some of the division leaders! That, to me, isn't necessarily a wild card, but another great team deserving of a playoff spot. A seventh super team to add to the division leaders. The variation now would be that all major league teams would be lumped together here to determine this one team, with the winner entering the playoffs of what ever league it came from. It certainly would make inter league play more important!
This would be in play for all but six teams.
See, I want a new Wild Card division that is really and truly made up of wild cards! Let's get to it.
In devising this second new division, I first look to certain other sports around the world (say Italy's Soccer League) where the last place teams in the A division are dropped to the B division each year. Technically that would be equivalent to say the Royals being dropped to Triple A, but we'll just use it as a basis.
Under my new system, every last place team in MLB would be dropped into this new Wild Card Division as a separately aligned division. Six total teams would compete here, more than the others which would now all have four teams (four better teams). Simply, the first place team at the end of the season is declared the Wild Card with a chance to play in the playoffs. Now that would be a true wild card. From last to playoffs! Certainly would make it even more interesting, and I'm sure low-tier owners would salivate at this.
To further it past year one, each season the records of the WC teams are compared to those of the divisions from where they originated, and if these WC teams have better records than those of the last place teams, then they move back to said division and the new last place team moves to the WC.
Let's line it up based on last year's records as an example. What you don't see at the bottom is that I first moved the Astros and D'Backs as planned, but in doing so they became the bottom two teams of their new divisions, and so they are moved to the WCD.

So what would have been different was that the Astros would've made the playoffs and the Rockies would have stayed home. Pretty interesting. You might say, "but the Astros totally don't deserve to be there!" To which I would counter that with, "but they beat 5 other teams to do it, while every other playoff team (save the Super Seventh) only had to fend off three!"
I think this is a much better realignment scenario than what has been "floated", and utilizes the Wild Card system in a new and unique way, not to mention gives fans of even the most bottom feeder of teams new hope that they too can see a World Series in their lifetime!
Well, that's what I've got. Now, I'll wait and see what MLB really does. At least put five teams in each league already! Sheesh!