Yes, there's no doubt that Kevin O'Leary's suggestion of selling off Senate appointments is nothing short of asinine.
That's not so much because the idea is inherently unconstitutional, but because of its substantive implications. The sale of Senate seats it would involve institutionalizing the worst aspects of the Senate's historical purpose (creating a systemic on behalf of the wealthy against democratic decision-making) and practical use (to reward people based on their ability to shovel money into the political system).
But it's worth noting that the reason O'Leary is in a position to make the proposal at all is the continued existence of a legislative chamber which lacks both a check against abuses in appointments, and any coherent purpose.
At best, any explanation for the continued existence of the Senate (beyond complaints about the difficulty of amending the Constitution) tend to involve the fact that it includes some well-regarded public servants who sometimes use their authority to carry out useful research and analysis of public policy.
But that's a role which precisely the same people could engage in within their own areas of expertise through other structures, without their simultaneously receiving both a lifetime appointment and the ability to generally control the passage of legislation. And so "but sometimes it does good work!" doesn't serve as a particularly compelling argument for the Senate.
Meanwhile, O'Leary's scheme represents a new - yet entirely plausible - worst-case scenario.
To date, the worst the Senate has had to offer is partisanship run amok: appointees whose first and only loyalty is to to the political goals of the Prime Minister, resulting in little check on longstanding governments and potentially insurmountable obstacles to legislative action by new ones, as well as the occasional obstruction of legislation passed by our elected representatives.
But O'Leary looks to be treating the Senate much as Donald Trump views the U.S.' cabinet: a source of substantial formal power without the constraints of democratic processes, which can be parceled out for the benefit of his corporate cronies. And it's frightening to think what could happen if O'Leary were to get his way, as the wealthy few who could afford to bid on seats would be able to secure the formal capacity to block any public policy which sought to serve any interests rather than their own.
Unfortunately, the Senate as it stands is plainly vulnerable to the whims of a Prime Minister who wants to use it for plutocratic ends. And we'd best ask whether that's something we're prepared to leave in place before O'Leary has sold enough seats to block any potential change.