There are 3 intertwined issues in this article:
1) Borrowing to invest. Something many investors could do, but most should not do.
2) Market timing. He did well on the buy decision, but only time will tell if this is a good time to sell. A better approach for most investors (those mere mortals that are not prescient or lucky) is to pick an asset allocation that is compatible with their risk tolerance and timeline and re-balance back to it periodically
3) How to react to rumours about investment tax changes. If an investor that is not heavily leveraged cashes out now to avoid possible CG tax increase, what do they do with the cash? Will they really be able to reinvest for an increased future return considering the tax they will pay now? It's possible to run some scenarios on various guesses of tax rate changes, but just selling on a hunch is not the way good investors  investors stay successful.