Don, if you look back, you'll see that what is going to happen is I'm going to send out a group email to all that expressed interest and give them a chance to make a firm commitment. That will allow me to order the proper amount of parts and not have a pile of expensive and unused parts. 
John, knowing how at times some forumites have posted they would buy things and then when it's available - they don't follow through, since you aren't yet certain of what the cost will be, might I suggest you require a partial, nonrefundable, upfront deposit when they commit to buying one, sort of like a pre-order. Otherwise, you might possibly find yourself with a sizable amount of "I want one"s which go unclaimed and unbought.
That's part of the plan. Since the parts cost for this unit is over $50 before any work goes into it, that's probably in the ballpark of what that deposit will be. After the run is finished, the design files will be available for anyone that wants to fabricate one themselves.
Would there be an advantage using this on a layout that's currently working okay so that it'll already be installed for future layout expansion or can too strong a tmcc signal be harmful having a detrimental, adverse effect causing problems and issues on a layout, sort of like "anything done to excess or too much of a good thing can be bad for you"?
I don't see any advantage to installing one on a properly working layout. I don't know that it would do any harm, but I don't have any actual data to back up that belief. My feeling is you install this box is a last resort after you've run grounding wires and insured your track and connections are in good shape. The major issue this solves is for large layouts with lots of track, there is excessive capacitive coupling to earth ground, that causes the amplitude of the TMCC signal to be too low for reliable operation. The box is a low impedance buffer that is capable of driving high capacitance loads without losing amplitude. It also provides some amplification of the signal voltage.
