My Comotion Speedster has a 1 and 1/8 steer tube.

So far found the Comotion fork and the Wound up.

Any others?

I plan on using the current woundup fork(for road brakes) on my Trek T1000.

Then adding a disk brake to the front of my comotion and a disk to the back of the Trek.

So, are you looking for a fork for a disc brake or a V-brake? I believe the stock fork length on the Co-Mo Speedster is 390mm. If you go any longer or shorter than this then it'll affect the handling slightly, the trail is the measurement you need to calculate, which can be calculated here if you have all the input data.

The change in the rake of your current fork vs the rake of a proposed replacement will make a difference in handling. Depending on the numbers, 5 mm change in rake can make a big difference in the handling of the bike. On the other hand a 5 mm change in the height of the fork will not change the head tube angle and steering feel much. To complicate matters the two changes can either offset each other or have a cumulative effect.

You can get used to most changes but be aware of possible problems by comparing the new forks specs to the old fork.

Disk fork.

This tandem came with the wound up.

I guess I should call comotion to see how their fork compares to the wound up?

Am I correct in the assumption that the Enve will only work with a tapered head tube?

If your Speedster has the older, external 1 1/8" headset then you can only use a straight, non-tapered 1 1/8" fork in there, which would rule out the Enve model.

Woundups come in more than one rake so it would be good to ask Comotion how they ordered the wound ups used on their new bikes. Most likely it is similar to the Comotion branded fork they sell now.