I'm sure Nintendo will continue to talk about sales of the "3DS family," so I'd say yes, they should be combined.
I think one of the key factors is that the introduction of the New 3DS and New 3DS exclusives is not going to 'kill off' the 3DS. Even if the original 3DS hardware is discontinued, there will still be new (with a lowercase n) 3DS games being made that are compatible with it. Probably most 3DS games released after the release of the New 3DS will still work on original 3DS systems.
That's reliant on this being a one-time thing like the DSi. If Nintendo keeps iterating on the 3DS hardware every couple of years, they're going to find themselves on the same slippery slope as Apple, who usually combines every iPhone sold in the past 7 years, despite the phone having drastically different specs and features from an iteration just a few years before or after.
