I'd start by visiting a local rubbish tip, looking in the e-waste bin, and taking an inventory. Any R2R rules would only need to cover, say, 80% of the weight of that bin's contents in order to achieve a really worthwhile goal. Anything representing less weight of rubbish than that would fall into the 'restrictions do more harm than good' category, which would exempt almost anything that isn't a consumer item, and spare the electronics industry as a whole an enormous weight of bureaucracy and restrictions for minimal gain.
What's left? TVs, washing machines, fridges, microwaves, etc. All kinds of stuff that can be - and therefore usually is - built down to an absolute minimum price with no regard for longevity or serviceability.
Here I completely agree, there's no good reason why spare parts shouldn't be routinely made available, kept available for a reasonable amount of time after a product has been discontinued, and supplied at reasonable cost to anyone and everyone as a matter of routine.
However, by weight, volume, or any other metric that can be meaninfully applied to e-waste, I don't think there's any real benefit to applying similar restrictions to lab equipment and similar. Landfill sites are simply not full of old scopes and power supplies; they're full of crap, bottom-of-the-barrel brand consumer goods that have lasted their 2 yr warranties and then died.