I would argue the biggest threat to coinbase is another crypto winter where volumes fall by 90%! And eventually the asset class becoming mature, so fees also fall by another 90%
The question is when? After what BTCUSD price? We’ll probably run the bull a few more months and then crash.
And then start all again.
Are we talking fees for coinbase pro, or the spot price offered by coinbase on their website? The prices for the former are already pretty low, with most exchanges charging around 0.2% on their lowest volume tier. The prices for the latter might be high, but I can totally imagine it staying high considering that forex rates at your local bank is equally as bad (around 1-2%). As a point of comparison for both, transferwise charges 0.4% for converting euro to usd.