the market has been wide open for eight years, but third-party router support is few and far between at best.
Considering all that, what makes you think 2027 will suddenly be the year of third-party Time Machine support?
Third-party router support for Time Machine is not universal, but it hasn't been uncommon, either.
While some manufacturers (most notably Netgear) apparently have dropped Time Machine support in recent years, others support it on multiple models (TP Link, ASUS, others). In the latter cases, you need to attach a USB drive to the router and use the router's software to configure the drive. Most routers supplied by Internet service providers do not support Time Machine.
As I mentioned, there also are open-source alternatives to vendor-supplied router software that can be configured to use Time Machine, though that approach can be too technical for many people to set up, and not all routers will work with these alternatives.
Another alternative is to get a network-attached storage (NAS) device. Most will support Time Machine out of the box. I've used a Western Digital My Cloud EX2 Ultra without trouble for a few years as a Time Capsule replacement.
The main caveat, and
it is a big one, is that most of the routers and NAS devices I mentioned currently support only the older variety of Time Machine over the Apple Filing Protocol. As a result, they will not work with macOS 27 unless they receive software updates from their manufacturers to use the newer SMB3 method. You also can't set them up for new Time Machine backups from macOS 26 Tahoe, but they generally work fine with older versions of macOS.
All of that said, if I absolutely needed a Time Capsule replacement today that could support Time Machine backups from macOS 27 clients with a minimum of fuss, I'd look for a cheap Mac (used or new) with a few more years of support ahead of it, connect a suitable USB drive to it, and set it up as a shared Time Machine server. A mini or maybe even a Neo would be particularly interesting for that purpose.