Wouldn't totally surprise me.
Miami will also have some serious cap space next year so I can this happening.
This isn't even remotely true. At present, Miami is projected to be about $10 million over the cap. Sure, it's all early termination clauses and player options, but still. Is Bosh going to opt out of his $20.5 million next year and $22.1 million the year after? No way is he getting that again if he tests free agency. Wade's $20.1 and $21.6 million over two years? Ditto for him, if not more so given his knee. Really the only one who might opt out is LeBron. If he does, the Heat will be at most $10 million under the cap, and there's no way in this universe that LeBron and Melo split $10 million between them. Heck, suppose Wade also opts out, because he feels like he isn't performing up to his contract. You think Melo, LeBron, and Wade can split $30 million between them (less once you account for roster holds and that this estimate assumes the salary cap jumps over $4 million next year)?
Melo is not going to Miami, end of story. Please don't scare people/engender conspiracy theories. Miami has nothing resembling significant cap room next year, even if LeBron leaves.