I know some people who actively seek out opportunities to MS. However, I believe that the vast majority of mile chasers follow the letter (if not the spirit) of rules set by the bank. This minimises the risk of clawbacks from banks. Loopholes get closed eventually as no bank likes being cheated. To assess the first half of the question - it is, however, possible to travel in premium cabins (perhaps once a quarter), if you spend enough, intelligently, and exclusively on 4mpd cards (disregarding sign-up bonuses in the spirit of the question)! 100k miles round-trip in business (a generalisation, of course, this varies depending on where you're flying) is 25k spend on 4mpd cards, which if divided across 3 months is about 8k spend a month - you can get more than 8k worth of 4mpd through a series of cards - WWMC (2k), VS (2k), PPV (1k), TR Pink & Blue (2k), CRV (1k), CRMC (1k). If you're earning a sizeable amount every month and finding a way to spend it exclusively on 4mpd cards, then you probably deserve to fly premium cabins 😅 Cheers!