Probably nothing uses 10Mbps these days now
At $DAYJOB we're still buying and installing a particular 10BASE-T device that's been in continuous production since the days when that was the "fast" speed, used by customers with the cash to upgrade beyond 10BASE2.
Why has it never been upgraded to faster Ethernet, you ask? Because it's a translator to even slower interfaces, RS-232 serial, remote-control IR, and human-pressed button contact closures. More speed would just let those interfaces get back to waiting for I/O faster.
The only reason it would be nice to make the Ethernet interface faster is that to do it, you'd have to make the CPU powerful enough to choke down all the noise you get on modern networks. (Broadcast storms, leaky multicast filtering, etc.)
Our most-used solution to that problem is to put it on the second network interface of the only server that needs to speak to it, creating a 2-node private LAN between them. The server then relays the information to/from the little 10BASE-T box, acting as a sort of Ethernet speed translator. The biggest problem with this option is that our preferred vendor's server motherboards have started to come with Ethernet ports that won't even speak 10BASE-T or 100BASE-T any more, so we can't use MDI-X; we have to add a switch to act as a media converter instead, even though it's only there to bridge two nodes. (And yes, it's an RB260GS lately.)
Our second-most used solution, when the 10BASE-T box can't be co-located with the server in the rack, is to put a hEX S in front of it to shield it from the rest of the network. It's configured as a firewall to keep the extraneous network noise from spamming the poor little box off the network.
And our third option is to convince site IT to configure their smart switches the same way as our canned hEX S configuration. Those of you who make a living as network engineers might think would be the best option, but it's always too much arm-twisting to get it done, so we've come to this pass. It's one of those "its faster to do it yourself than ask someone else to do it for you" things. Since our time isn't free, adding an RB260GS or a hEX S — depending on whether we need firewalling and intelligent traffic shaping or not — is cheaper all around.
any 1/2.5/5/10 Gbps RJ45 port effectively has to support 100Mbps
The gigabit-only ports on the servers I mention don't follow your logic because Ⓐ servers don't need WOL, being awake 24/7; and Ⓑ the energy use of the Ethernet ports is nothing when there's a honkin' Xeon processor on the other side of it.