Once Gingerbread appears on the Nexus One, it clears the main major step to putting it on all Snapdragon phones.
The next step is to put it on all HTC phones that doesn't have carrier permission, like the HTC Desire, Desire S, international Incredible S, Desire Z and Desire HD.
Since the Nexus One uses the Qualcomm 8250, it means the 8250 powered phones will get it first, ergo, Desire, Droid Incredible, EVO. For the latter two, just the carrier permission.
Then the task heads to putting Gingerbread on the Qualcomm 7230, 8255 and the OMAP36xx chips. Once you get the new OS version out on a representative phone of each particular chip, the rest would follow assuming carrier permission.
Please note that seems Gingerbread first came out on the Hummingbird processor, the Galaxy S and Tab actually has a head start in getting this.
That is really how the true pattern of the OS updates go --- first processor to get the new Android OS, tends to have the phones using the chip to follow it. During Froyo's turn, it was Snapdragon 8250 (Nexus One), followed by OMAP36xx (Droid 2), then the Snapdragon 7230 (T-Mobile G2), then Snapdragon 8255 (Desire HD) and the Hummingbird trailed. Guess whose phones got Froyo updates last? Whoever gets and makes the Nexus or the flagship device actually has the first call advantage for the next Android OS version on their chosen processor. No surprise, Samsung wants the first base now, which lead to the Nexus S (Hummingbird).
In any case, Xoom, with the Tegra2, got the jackpot for Honeycomb. It will take a little while before Honeycomb gets to OMAP44xx, dual core Snapdragons and the like.
At the same time, you cannot have simultaneous development of the OS for all processors --- its likely to mess things up. You need to pick a platform, work, debug and perfect the OS on it, then when its ready and hardened, spread it out in other platforms. That's truly the proper development cycle for all these things. Debugging is the most tedious part in OS development, and you cannot have simultaneous multiple chip factors. You need to control all these factors. You cannot blame Google for what they are doing --- they are doing the most logical solution to the multi platform situation.
In any case, the job is done for the Qualcomm 8250, and that is symbolized by the Nexus One updates. Its the easy road ahead for the rest of the 8250 powered phones, like the Desire, Droid Incredible and HTC EVO. All it takes now is the carrier permission.