Agree, that Suzuki's R&D and tooling for the LS650 has been long paid for, but since it's likely that the Savage/S40 isn't a
volume seller, is seen by many motorcyclsts as a "Beginner" Bike (though not by most members of this Forum

) and generally doesn't get any press from m/c trade publications, I can't help but wonder how it's "doing" for the Company?
'Zuki is already in bed with Kawi on the 1600 Mean Streak/Marauder models ... and as pointed out, has their SV650 & 1000 powerplants in several Hyosung models ... so it isn't inconceivable that any R&D and/or re-tooling req'd for a new 650cc model would be shared with either of the 2 aforementioned manufacturers ... right now, the Savage/S40's three closest compeditors in the Cruiser marketplace are Kawi's EN500 Vulcan, Honda's VLX600 and Yami's 650 V-Star siblings ... the Star(s) and the VLX being v-twins ... and all weigh more than the Savage, so power/weight ratio may actually less than the LS650's 33HP/352lbs (I have no idea of the figures for the other Bikes ... though I know that the EN500 is actually faster than many 750cc Cruisers ...).
So, all that being said, I too wouldn't be surprised if the eventual successor to our dear Thumper will be a v-twin ... possibly a joint effort (the Baby Vulcan is due for a replacement) ... and possibly either a direct compeditor for the 650 V-Star Classic or an entry-level "Power Cruiser" using the SV650 mill, similar to the Hyosung.
Personally, I'd like to see Suzuki maintain the unique "Big Single" ... just keep upgrading the current platform with an easier to remove tank and/or easier spark plug access, a bar mounted speedo with a trip-meter, and a fresher "Custom" styling ...