As much as it pains me to say it, Cloudflare seems well positioned to eat ngrok's lunch. AFAIK they offer everything ngrok does plus auto TLS certs, CDN, domain name registration, and tons of other features. They also have way more edge servers for terminating tunnels close to the origin devices. And they can afford to do all this for free as a loss leader product. It's the AWS bundling effect. Oh and the client source code is available.
I don't want to see Cloudflare completely take over this space, but Cloudflare Tunnel is tough to compete with.
One knob ngrok could still turn is adding auto TLS certs which are managed on the client side. Then you can offer e2ee which is something Cloudflare will probably never do.