So I recently switched from Fidelity to Vanguard for a few reasons, but it was partly to harvest tax losses. My portfolio isn't significantly different or anything, and I still have an (empty) Fidelity account.
This got me thinking, if I hold essentially the same assets (but based on different indices- CRSP vs S&P vs Russell etc.) in funds at both Vanguard and Fidelity, I might be able to seamlessly and more frequently harvest tax losses. I could contribute solely to one account or the other in 3 or 6 month periods and switch off. Whenever the market takes a decent dip, I sell part of whichever account has a higher cost basis and transfer to the other one.
If I avoid transaction costs by holding for whatever the necessary penalty-free period, maybe I could accumulate significant carryforward deductions. It's late and I'm pretty out of it, so am I missing something arbitrary here?