I feel you with the iconic units, but Protoss gameplay is going to be totally evolved with the new units they're getting. Stargate openings are going to take a completely different meaning with HotS. Recall will allow for new early aggression builds that Protosses can't currently do because if they do it now, it's basically all-in. They'll have a host of new openings where they can mix aggression with recall, greedy early expansion builds with the mothership core purifier, and even harass openings with Stargate using Oracle/Phoenix.
Going further, the Tempest is actually really awesome for a Tier 3 unit too, because P's will likely almost surely have Stargate tech out anyway by the time they hit the lategame that it would be a pretty natural transition. A group of 4-5 Tempests with the range upgrade will be great for sniping opposing lategame units from distance in engagements. They'll be great for sniping Colossus or HT/Archons in PvP, Broodlords, Vipers, Swarm Hosts or Infestors in PvZ, etc.
I personally hate the Colossus and think it's boring as hell and would rather have the Reaver, it's just way more interesting. But for Carrier vs. Tempest, there's really no way to make the Carrier a good unit without making it too strong. If you increase its range and/or speed/acceleration so that Vikings/Corruptors don't own them, it becomes way too good because of its insanely high DPS. Also interceptors are always going to be terrible versus Marines no matter what you do, and Hydras now that Zerg will be using them a lot once they hit Hive.
The Carrier is just a unit that even if you buff it to be worthwhile, will either be too good in certain situations or terrible in others, and that's not what you want. The Tempest is a really cool concept, will add tons of micro to the game for BOTH players, and has tons of different uses. So while nostalgia would tell you that keeping the Carrier is a must, it's really just a unit that doesn't fit in with Starcraft 2.