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I'll update this if I find more. For now, this seems to be a partial solution. It's a Gmail add on (except I don't use Gmail) that adds reminders. The options when setting reminders include cancelling it if someone replies, and to remind everyone in the thread. If you combine those two, it seems like — if you use Gmail's web client and have $23/month you're dying to get rid of — a decent way to add the feature. Source: over 1 year ago
Facebook - Connect with friends, family and other people you know. Share photos and videos, send messages and get updates.
FollowUpThen - The simplest way to schedule an email reminder
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Gmelius - Gmelius is the first collaboration platform designed for G Suite and your company's daily tools.
Mastodon - Mastodon is a decentralized, open source social network. This is just one part of the network, run by the main developers of the project It is not focused on any particular niche interest - everyone is welcome!
Right Inbox - Schedule Emails in Gmail To Be Sent Later