Yeah all valid points.It is not really a "entire product line". In terms of the Mac, the iMac and Mac Pro are the only mac systems that come with a discrete keyboard and mouse (**) . (kind of odd Apple puts both in the box with the rack mount version. That likely is a 'waste' over the aggregate systems sold. However, some folks use the rack version tipped sideways as a desk-side version so not always a waste. I can somewhat see why they do it. ) It would expect the keyboard and mice to be almost identical. (the port and a few power management chips inside the only difference). They probably will not have both Lightning and USB-C ports on them. Once they have a USB-C one there is little good reason to keep the Lighting one around. Folks would only need to buy a general USB-C (or A)-to-Lightning cable to charge the 'old ones'. If they have had an older iPhone/iPad how likely is it that folks don't already own one of those cables? ( millions of folks already have these. Especially old keyboard/mouse users. ) Apple is likely going to want to sell the new units at maximum volume.
Apple used the "same cable" for the iPhones as the keyboard/mouse. Well Apple is deep into transitioning the whole iPhone line up to USB-C. Same with the iPad line up. Mac laptop line up ... many (although MagSafe is back). Lots of folks are already have USB-C cables even if been in the Mac ecosystem for a while.
For typing and pointing product line the "Magic Trackpad" needs an update also. ( two keyboards, mouse , and Trackpad ) all in one shot.
** The Mac Pro 2013 skipped the keyboard. In part, because the box was relatively small. For a long while it was only the iMac.
[ Maybe there is a new mouse to adjust so that can use it while plugged up. I suspect they are going to stick with the that "hide the port, it is magical in appearance " dogma though. If there is a redesign that is likely part of the delay. ]
I strongly suspect Apple sells at least an order of magnitude more AirPod containers than they do keyboards and mice. There is way more inertia to get over there than with the keyboard. Plus these "touch ID" keyboards have been relatively new ( given average service life Apple assigns to selling their keyboard mice. Apple goes many years with no changes. ). Pretty good chance they will stretch these "new-ish" Lightning ones out to the 'last minute' and flip them just in time to avoid EU drama. Use most of 2024 to draw down inventories to as low as possible.
But there is some stronger argument in updating the Magic Mouse and Keyboard these days, due to one changed reality: both the keyboard and mouse are supported in iPadOS. There could be incentive there to make the more compatible, like integrating the TouchID function.
Don't forget about the Mac Studio and Mac Mini too; though they're not in the box, Apple recommends them when buying on the store. For the Studio and Pro, they sell the black one.