while it is obviously possible to grab triads (or just two notes of a chord or adding a fourth note, etc.) all around the neck in any tuning (just as one does outside of open positions in standard - altho, what else is an open position chord... ), i think it is important to remember the point - already made above - that alternate tunings are typically specific in their function. which is to say that one would choose drop-d because it suits the composition. if a g chord (in open position or elsewhere on the neck) is most important to the composition, it is perhaps possible that drop d is not the most, i dunno, let's say 'convenient environment' for the tune? of course that logic has limitations; just thought it was important to restate.
(typically, in drop d, when i need a g and am playing around open positions, i will just pluck the g (5th fret) on the 6th string and have a b, g and d available on open strings 2, 3, and 4, as many have already mentioned.
if i was noodling around in drop d and was wanting notes from the g chord often because i accidentally stumbled on a phrase i liked that used g as the 'anchor' (tonic?) and not d, i may get irritated if it was complicated enough and tune to open g and try to find the little phrase i was messing around with over there... the "math" does make my head hurt and i tend to want to avoid it for sure, but i think it would help me to understand music better to do it more often [easier said than done
]. - p.s. i suppose one could also tune to standard in that example, probably be a much easier transition actually, i am just more used to playing in open tunings)
(i would recommend figuring out the shapes for any tuning for yourself by the way, instead of relying on books and videos etc. again, easier said than done...
(thanks for all the cool fingering photos, Larry. i laughed out loud upon reading 'a very gutsy d'
)
hope some of this is helpful. it is fun to experiment with new tunings. hope you are enjoying your experience.