Hi
It would actually be really easy to switch the gain toggle for a footswitch.
You would need to move up to the next "box size" which would be a 1590 BB or similar, perhaps a larger one if you want 3 footswitches. Hammond make a popular size called 1590XX which I use for lovetone clones which is about 145 x 120mm
You could then remove the toggle switch that is used for the low/hi gain mode and wire in a footswitch - you can simply add an LED to this too.
For me this would work quite well, as I find that if I set everything else right, you can get a good compromise between a light OD and a heavy OD by simply just flipping the toggle, so takes out the need for 2 gain pots.
However, if you just want two different "gain pots", you would keep the toggle for the mode, and then remove the potentiometer that controls gain from the Elements PCB.
The you would wire the pot pads on the pcb to a switch, which itself if feeding off to two different pots.
similiar idea here:
if you wanted to go extra-crazy, you could have the gain mode on a footswitch too - so switcable mode and switchable gain setting for each mode = 4 levels of gain control. Awesome.
Adding a boost pedal is as easy as deciuding what boost you like, fabricating that circuit (vero, any number of PCB fabs from Madbean etc) and building that in as you would any other pedal.
Adding an order change switch is a bit more complex. To do this you would need to remove the board mount in/out hardware from the Elements PCB to allow you to wire the 3PDT "flipper" toggle to the Elements.
similar to this:

You can read up more, here:
http://www.madbeanpedals.com/forum/inde ... pic=4169.0
As has been noted, the expression jack only changes the mix of gain with clean, NOT the amount of Gain.
I think the easiest option is to just trade out the toggle for a footswitch for the gain... Its the least amount of fucking around.
I considered going down this path, but just purchased a second elements. The pedal is so beautiful I didnt want to desecrate it.
You could always ask Ryan if he ever just builds the PCB, then get a talented builder here to finish it in the box of your choice. In fact, if Ryan would do that, get him to leave the old gain toggle and/or pot unpopulated so you dont have to desolder it. That way you wouldnt be paying for a beautiful box either. I reckon he might be amenble to that.
Ian