OK I will try to answer a couple of the questions here. I dont want to just update the original Magicworld as there are mods that we want to remove however I dont want to force this change on people. I would much rather give them a choice. It costs us nothing to have 2 Magicworld packs on the server and people can then choose which one they want to play with. As far as I know, both Magicworld and Techworld are considered stable (if there is such a thing in modded Minecraft) . I suspect these 2 packs will be locked down and called final very shortly. (that call hasnt been made yet though)
This is the thing with making modpacks. It is not just the mods that evolve, we do as well (at least I hope so). The early packs were essentially made as filler packs to help whilst we waited for mods to come along which allowed us to make the packs we wanted to make (Ultimate). Mods were put in these packs that shouldn't really have been there (Thermal Expansion in Magicworld being a great example). The next pack which be a much better experience I hope.
To the best of my knowledge there are no current plans to update the Direwolf20 pack in 1.5. At least not until all mods that are in the pack have been updated.
Yes, Tinkers Construct is planned for the 1.5 preview pack (please dont read to much into this name, we just have no idea what to actually call it as nothing is quite right.)
As to world reboots, we want to minimize the need for that as much as we possibly can. However we cannot hold off updating packs for ever. At some point you need to add a cut off date and just roll with it. We are not there yet though with our packs, however I do want to update as soon as I feel we can. Right now that looks like several weeks after 1.6's release, so current owners can make plans accordingly.