I've thought about this idea quite a bit, and may still try to do something in my own house. The big issue, as with all heat recovery efforts, is timing. You've already indicated you've thought of that one by mentioning clothes washing while showering. The obvious first approach is to create a thermal reservoir to hold the recovered heat until it's needed, but that encompasses a lot of issues in itself.
My plan, if I do it, is to build my own drain water heat exchanger from ABS and copper. Now that my final plumbing inspection has been completed I can install an non-NSF, non-UPC, labeled device! I don't have a vertical drop available, like you do, to utilize one of the commercially available vertical heat exchangers. As to the timing issue what I will do is route the cold water supply to the shower through the heat exchanger. That is the one use of water where an exchange from the waste to the supply can be done simultaneous with the use. Showering is also the greatest use of hot water. I've decided the effort to recover heat from the dishwasher and washing machine drains isn't worth the hassle of storing the heat until it can be used.
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