interesting ideas. i hate to make you keep talking to yourself in here, so ill add my two cents.
depending on the actual implimentation, i could see this working out OK, or possibly working out not very well. heres some of my reasoning...
-i dont think that your calandria is going to do anything besides get in the way at best, or cause problems for your pump at worst. calandrias in large breweries operate under a pressure differential which is created by the weight of the liquid column. in a 20 barrel tank, there will be many PSI difference between the top and bottom, so that the flow is self-regulated in a single direction. in a small 15 gallon pot, there is barely 1psi of difference, so the water is not compressed (and the boiling point isnt sufficiently raised) in the heater, and the flow is not self regulated in a single direction. meaning if wort were to boil in the heater, it could more easily overwhelm the pump and cause the flow to go backwards.
-the relatively large volume of liquid below the pump and heater is going to be fairly stagnant (especially if filled with trub or protein precipitate or other solid particles, making the fluid in this area thicker). this area could possibly retain wort that hasnt had the DMS adequately evaporated, and could effect flavor of resulting beer if it were to mix after boiling.
-your kettle opening/vent is undersized (atleast in the drawings). in large breweries, the updraft of hot air, or alternaltely a fan, gives a large amount of suction up the exhaust stack. in your smaller kettle, there is going to be very little updraft, and the only amount of air movement is going to be caused by the volume of steam created by boiling (no suction). also, this promotes condensation, which if left to drip back into the kettle, pretty much negates the whole reason for boiling in the first place (reduction of DMS; it will recondense and just drip back in).