no customization

Like overmind suggested, if a mission requires Dropships, it is likely that you can just start the mission with Dropships- for example, you're taking control of a base that happens to be able to build them (The Dominion's Dropship Fleet Yard!) Perhaps your troops are shuttled in with a set of Dropships, and if you can't build more, you'd better keep those ones alive.

If they are necessary, and for some reason the level won't supply them, it may well be that Blizzard will make it so you can't even attempt the level until you've met the prerequisites. Be forced to play other missions? Probably. But it is not likely that storyline missions will require any exotic units that you wouldn't generally buy in the first place.

If Dropships aren't necessary- if you can get away with using air units, and lifting off a CC to expand, then the mission would just recommend them. The level will be on "hard mode" because of that, but it is not as if you don't have the opportunity to set it to "easy mode" by playing other missions.

In the case of most other units, there really aren't a lot of situations where you have to have them over the course of a level, assuming you have the same "expenditure" worth of units and upgrades.

 

I doubt there will be any island hopping missions. In another thread it was stated the island hop games unevened the game thus making it harder for Zerg and Protoss while easier for Terran, becuse somewhere I heard the nydus worm was removed.

 

Firstly, where are you pulling these numbers from? You have no idea how much Dropships would cost, nor how much each mission may give. There are a couple of points to back up that it may in fact be fairly cheap, too.

1. Seeing as it's a necessary unit, not a luxury, chances are that it would have a relatively low cost for its effectiveness. Just like how you'd be given SCV's and Marines for free, what with them being the most necessary units in the game, but buying Battlecruisers and Thors would cost a relative fortune.

2. To keep the game flowing, and the shop system interesting, the idea of needing to play three games before you're able to acquire another unit is ludicrous. If you needed to play three missions before you're able to afford the next unit, then the system of suggesting which unit to buy for the next mission is useless, as you'd always have to play separate supposed side missions in between each game.

No you're not, you're just ignoring everything else I said. You may had noticed I wrote that it's a non-linear campaign, so even if you are strictly following the main storyline, there isn't a 'next' mission. You'll be able to do other missions which follow the main story. It's not just one main mission after another main mission after another, with a whole bunch of extras on the side.

Perhaps I didn't make it blatant enough. To restate what I said, simply saying you don't like that idea because you'll have to play other missions until you can afford the Dropship is like saying you simply don't like having the option of failing a mission because you don't want to have to redo it all over again.