I don't see this as a great idea, but it's not necessarily a bad one either.
Suppose you have some money in an HSA and you have a $1,000 medical bill. As long as you keep that receipt, you have the right to withdraw $1,000 tax-free from your HSA at any time.
You could do that, take the $1,000 out of your HSA, and then deposit $1,000 into a Roth IRA (assuming you meet the income requirements to do so). At that point, you would then have the right to withdraw $1,000 tax-free from your Roth IRA at any time.
Either way, you have $1,000 in a tax-sheltered account that you are free to withdraw at any time. The difference is in what happens to the growth on the $1,000 while it's in the account.
In the case of the HSA, any part of the balance can be withdrawn tax-free at any age if you have medical expenses corresponding to each tax-free withdrawal. If you are fortunate enough to remain healthy and you wish to access the growth on your $1,000 without a corresponding medical bill, you'll pay tax at your current marginal rate (at any age) plus a 20% penalty (if under age 65).
How does this compare to the Roth IRA? Earnings in your Roth IRA can be removed tax-free at age 59½ regardless of medical expenses. Before that, you'll generally be taxed at your current marginal rate on these distributions, plus a 10% early withdrawal tax.
Which one is better? Depends on when you expect to need the money and what you forecast your medical expenses to be. Prior to 59½, withdrawing from the HSA is better if you have medical bills (since it's completely tax-free in this case), but the Roth IRA is better otherwise (because the penalty for non-qualified withdrawals is only 10% instead of 20%). After 59½, the Roth IRA wins out because it's tax-free whether you have corresponding medical bills or not.