Practically no, but theortically yes.
Reasons
It is able to lengthen 67 without the worry for and duplications
as it extends from Tampines while service 2 just go directly to the
changi village via expo
In addition, the long route should not be a problem as some
service had even longer routes, see 51, 858 you will
understand.
However, service 67 is a SMRT service and it should not be
allowed by PTC to extend by Tampines as it would use Pasir Ris and
it would violate the districts boundary.
In addition, the demand of the route would not be as high, as
Changi Village Terminal is designed to serve the people going to
Pulau Ubin nd the few residents living there, there is already
enough links for the residents there and as not many people in
Tampines and along the route would frequent Pulau Ubin regulary,
the route may not be profitable and given SPH(SMRT CEO) attitude,
she would not like it.
However, it is possible to extend to Sengkang if you like
it.
This post by SBS n SMRT says that SMRT cannot go to Pasir
Ris and CVillage. In fact I proposed sv 67 be extended to CV. But
if no SMRT sv can go there, I don't see how 984 can work.
And I don't think going through Seletar would be very nice for
SMRT's buses(at least not the bendies). Seletar has a lot of narrow
roads, even some SBST drivers sometimes hit the kerbs there(I've
experienced that on 103M).
Just my two cents worth