The only problem I'd have with it is you'd just have to keep track of the cost basis for many many many transactions for tax purposes when you one day sell or spend the bitcoin in the future, so for that reason I certainly wouldn't want to be buying every minute or hour or even day, but some people might not mind that accounting headache.
I totally understand that. Where I live, there is no such thing as taxing transactions (apart from the VAT). I only pay wealth tax for the "wealth" I have on the 31th of December. If markets dip on the 1th of January, I still need to pay the 31th December worth of wealth.
Considering how often how many "exchanges" fly by night, claim to have been hacked, etc etc etc neither of the above-mentioned income systems seems to make much sense.
The more-real buying and selling when using "exchanges" is when you buy a positive balance entry in an exchange's database and when you sell your positive entry in their database for a purported output to a blockchain or to some other institution that sells positive-balance database-entries.
If at the end of some period the proceeds of your cashing out of all those various database-entries exceeds what you paid into such database-entry purveyors you have an income, assuming of course that the purported outputs ever actually arrived, which of course they do not always do.
It is just like playing world of warcraft really, does it make sense to try to keep track of every single time you managed to loot some monster or treasure-chest or dungeon, or, rather, to simply compare how much it cost you to play the game versus how much you managed to sell the resulting accounts or loot for minus electricity and internet bills and maybe depreciation of your computing equipment?
Unless you actually do turn a profit overall, some tax regimes won't even let you write off the electricity and internet-connectivity and machine-depreciation and fraction of home your home-office you do it from, so until you do actually bring home in local spendable currency more than you spent it makes no sense even probably to try to work out any details at all. Only actual bottom line is income.
The wealth taxing idea though sounds weird and potentially dangerous. Politicians in Canada once upon a time threw around ideas along the lines of someone once sold one world of warcraft magick sword on e-bay thus anyone who ever finds such a sword in the game ought to be taxed for doing so, based on how much one person once somehow managed to convince someone to pay for one once upon a time. To be taxed on such "wealth" even before you managed to actually sell it, wow, seems horribly draconian. Property tax on virtual property / database entries / magick swords?
Scary, maybe especially so to someone who can "create" maxint magic swords with a few keystrokes...
Maybe RAM should be taxed based on how many billions of dollars a byte could be if it were used to represent billions of dollars? Insanity.
-MarkM-