On the contrary, I feel like both boys should return. Mother barely gets any representation in Smash Bros as is, and I feel like cutting one of the two would be cutting out an entire part of the series' history filled with things they can use. Like the Pigmask Soldiers as enemies in Smash Run, etc.
However, Sakurai has been soo hush hush about the franchise, which concerns me. :S
I've talked a lot about this in the past but I'm pretty sure both Mother boys are safe, especially Ness.
Ness:
1. Original 12 and in every game.
This is enough but just to add more to it:
2. Earthbound re-release on the Wii U was a huge success.
Now for Lucas:
1. No starting roster character has yet to be outright cut from a Smash game.
2. Only starting roster character from Brawl who hasn't been confirmed or strongly implied yet.
3. Relevancy argument no longer works with the return of Ike.
4. Semi clone argument doesn't work with the return of Toon Link, Brawl's biggest semi-clone.
5. Only character aside from ROB in the SSE that had any real character development.
6. Still the latest hero of the Mother franchise.
7. Only semi clone to ever be in the starting roster of a Smash game.
8. Ulimate Chimera mentioned on May 1st.
And for the both of them:
1. The Franklin Badge and Mr. Saturn have made the cut, strongly implying that there is going to be a Mother character in the starting roster.
2. An Earthbound stage in the Wii U version and a Mother 3 stage in the 3DS would make too much sense.
At this point, I wouldn't be concerned about either of them. The reason that not much has been said about Mother is because it's a small franchise (only three games) and hasn't had an installment since 2006 (which was a Japanese exclusive to boot). These things being said, it doesn't really need that much attention. Also, Mother is hardly the only franchise that hasn't gotten much love since the SSB4 site opened. DK, Star Fox, Yoshi, and Kirby haven't gotten that much attention either and they're considerably bigger. Also, keep in mind that Lucas was the third to last starting roster newcomer that was shown off to Brawl so for him to be revealed relatively late in nothing new to him.