The reason these colonies failed had to do with a factor already mentioned: resupply. Iceland and Greenland both relied on imports from Europe. They actually had a fascinating credit economy, where Icelandic settlers bought a years' worth of supply from Europe on credit, and then during the right season, paid it all off with sheep wool and some other stuff they produced there. For Greenland, it was the same deal, usually with Iceland as an intermediary, and with them providing loads of fish to pay for the stuff they got on credit.
The fact that Greenland went through an intermediary, and their margins were slimmer anyway, ensured that the colony there was always a barely-surviving frontier settlement-- and eventually was just abandoned.
In short: these colonies weren't capable of existing independently for a very long time. Iceland could exist comfortably, but only through trade with Europe. No trade, no Iceland. For Greenland, this was ultimately terminal.
American colonies had an even longer "way to go", far from Europe. Trade was almost impossible. To thrive, they'd need to rely on trade with the natives. A functional trading relationship demands a colony of at least a somewhat meaningful size. This is required, because they need to produce stuff. They can't sell stuff from Europe, because bringing it over isn't all that practical. (Otherwise, supplying these colonies would be possible!) Good as the Vikings were at sea-travel, the whole business of crossing the ocean wasn't yet as workable as it would later become. People structurally under-estimate how dangerous this kind of thing was. These Nordic loons managed it because they were some of the most daring madmen of their age.
Anyway, Iceland had population issues already, Greenland was a marginal outpost... and this tells you everything about the prospects for an even further-out American settlement. If it's established, the people there end up like the lost Roanoke Colony. That is: killed by the natives, assimilated by the natives, or dead from disease or starvation. Take your pick. Net result remains the same.
Conclusion: no, it wasn't all that plausible or simple. If it had been, the ballsy fuckers would have pulled it off. They didn't. Now, is it absolutely impossible? I'm not saying that. But you require really exceptional circumstances. In AH circles, this usually involves some kind of religious reason for a whole load of people (including many women) to permanently travel out in the mysterious West, in order to escape persecution.
Basically: Vikings doing what the Mormons did, but by ship. That's the way to go, if you want to do this.
