^ I-587 between Greenville and I-95 has independent utility.
I guess you missed the part where I said "these gaps wouldn't be allowed". I'd also require all new interstate segments to be contiguous. No gaps allowed. And that includes 3di routes connecting to their parent.
So... if it were up to you none of the newer sections of I-69 could be signed since there's no connection yet to the original I-69, and none of the newer sections of I-49 could be signed until the gap inside Shreveport is built. This is a lonely position you have.
It's better than what happened in NY with I-86, where there's the main segment west of US 220 and a short section east of Binghamton that was only designated because NYSDOT got tired of having to put back the sign covers, and will probably not connect in the foreseeable future, if ever.
Or I-74, which exists as two separate interstates because the portion connecting them will
never be built.
I-587 will also lead to a situation where there will be no satisfactory way to deal with I-795. Either it will have to have an otherwise pointless overlap (another no-no in my book) to meet its parent or it would be truncated and orphaned.
What's the point of even having a numbering system at all if it's disordered basically all the time because of stalled and cancelled projects? I like my route systems to be neat and tidy (along with everything else in life).