I hope the Edge series will also benefit from that code unification.

I'm missing from Garmin usage of Inertial Navigation System (INS [1]). The sensors are in the devices, accelerometers and gyroscopes. We've using them in airliners for decades (very basic INS was available with the B707, high quality from the B747/A300 onwards), in cheap car navigation (that's why you can drive through tunnels) and most smartphones (you've probably noticed that also your phone handles five kilometer long tunnels well). As far as I know, high quality INS could bring a B747 over the atlantic. My Edge has an accelermoeter and gyroscope but I see often straight lines in the mountains, in the city-center, in tunnels and garages and when the cloud coverage + trees work together. And it not just the recorded route, it is also the current speed and distance and precise turn-by-turn navigation.

Garmin, Wahoo, Karoo keep adding more of GNSS. GPS, GALILEO, BAIDU, GLONASS, GLONAS 5GHz, Multiband and ground stations (that approach failed). That improved the signal remitance somewheat but the mentioned natural conditions still interrupt or reduce that GNSS quality. Because it is external! External navigation depends on external guidance. You cannot fix that by adding more. And hostile elements figured out, that is easy to jam or spoof[2] the GNSS signals.

Using INS in combination with GNSS should work rather well on a roadbike. Usually mixing the signals from INS and GNSS depending on quality. Except where GNSS is turned off for reasons like jamming/spoofing e.g. in eastern europe. But usually INS needs only to cover a gap of 30 seconds to five minutes. INS is probably less useful on a mountainbike (vibrations and impacts) but especially in the woods GNSS fails...so maybe even here it can help. I think Garmin uses the sensors for other kind of metrics on mountainbikes already (I think the call it grit/flow?).

My smartphone handles a tunnel well. My bike-computer also should do it :)

[1] https://en.wikipedia.org/wiki/Inertial_navigation_system [2] At least GALILEO has some protection against spoofing?

PS: The integrated LTE-Modem could also benefit security in cycling. There was a sad incident during the last roadbike world-championships in switzerland and a life lost. Cycling computers detect crashes and can send SMS with coordinates but they need a smartphone (radio isn't allowed and smartphones aren't robust).