Tail emissions can help stabilize block production. Currently fees are very volatile, and going from almost no fees to very high fees and back doesn't lead to stable block production once the subsidy subsides. Will lead to reorgs and intermittent huge gaps between blocks. But we must keep the 21 million limit. So UTXOs should have an expiration date. UTXOs expire after 50 years, and they are added to the emissions schedule over the following 50 years. Thus the block reward doesn't go to zero and we stay under 21 million limit. You just have to move your BTC every 50 years.