US 201 north of Waterville would make more sense given that it connects towards roughly the same path as Autoroute 73 in Quebec. Not absolutely necessary, but makes more sense than extending I-95.
No, the most pressing need to promote to a 4-lane route would be US 1A east from Bangor to Ellsworth (and onward with ME 3 to the bridge to Mount Desert Island a/k/a Bar Harbor). It doesn't need to be divided -- the terrain makes it tough to do dual roadway, but a five lane Florida type might work... Head-on collisions with the current 2-lane and occasional passing lane 3-lane are really a problem though... Might need to do some new terrain sections, and such...
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Quebec might send A-73 someday down towards Lac Megantic and the border at Woburn: I've always envisioned a multinational route 102, a christened QC 102 cosigned on A-10, then running along QC 108 & 212 to Coburn Gore, and a new ME 102 or US 102 along ME 27, ME 16, US 201A, ME 139, I-95, I-395, 395 extension, ME 9, US 1 New Crossing... to NB 1 (cosigned as a new NB 102) and NB 2 into Nova Scotia with NS 102 replacing NS 104 west of current NS 102. A true 102 corridor 3M: Montreal - Maine - Maritimes, or Montreal - Halifax Highway...