This has been tried before. Indian Airlines (now merged into Air India) inducted A300's in the 70's for use on domestic metro routes and at one time had over 10 AB3's on domestic/SAARC routes.
Just before the merger, Indian Airlines did induct 2 A330-200's on lease to test out suitability for domestic routes just as the last AB3 (VT-EHD) left the fleet. But politics ensured that plan didnt take off. A fleet of Widebodies on metro routes would have enabled AI to maintain capacity on key metro sectors & redeploying the smaller A32S fleet to Tier-2 routes - many of which they have simply withdrawn from making way for 6E to take over.

Is it time to revisit the widebody idea esp with the market booming? Like with the AB3, the idea would be to deploy them on peak hour flights on BOM-DEL-CCU-MAA quadrangle with select additional routes to stations with traffic like BLR-TRV-SXR-GAU.

Back of paper calculation shows a small fleet of 6 A330-300 "regional" could free up 13 A32S's for use on other domestic routes where AI/IC has withdrawn from.
Question: The AB3 was the perfect size for this operation but with that ruled out, how suitable is the A330-200 for short-range (2-3 hour) high-frequency flights? With 18J seats in 2-2-2 layout with 40" pitch, How many economy seats can we squeeze into an A332 with a 30" pitch and 2-4-2 layout vs 3-3-3 layout? What are the corresponding figures for the A330-300 Regional? The higher cycles will have an impact on maintenance costs, but overall I think they would a huge CASM advantage?
Personally think the A330-300 is too large with over 400 seats. Around 300 seats with a 24 seat regional-J cabin would have been perfect sized. Time for Airbus to NEO the A300?