None of the currently available TLDs can replace .com, because they are either bad, or too expensive, or ccTLDs. The "replacement" needs to be stable, with no restrictions, cheap and totally generic. I've always thought .web might be the next big thing, but they would need to price it competitively ($5/y?) and refrain from the domainer-registry approach (no "registry premium" domains). Then and only then I think it will be a strong contender.