@cruiser If net gain from a principal residence exceeds $250K/$500K, the excess is treated and taxed as capital gain. This is long-standing law and nothing new.
The 3.8% is a net investment tax on interest, dividends, annuities, royalties, capital gains, rents (not derived in the ordinary course of an active trade or business), and other passive income, reduced by allocable deductions and offsetting losses.
The tax doesn’t automatically apply to any and all passive income; it’s determined by a convoluted formula that put different types of income into different “buckets” and takes a modified form of adjusted gross income into account. Thus, your statement that, ”Any amount over…$500,000…will now be taxed at 3.8%” [emphasis added] is incorrect.