Yes, there is a lot going on
with new materials and methods, but I don't see anytime soon something
to match wood in the strength/weight/price range, at least not with DIY
possibility. Most of the new development is esoteric, highly expensive
and need complicated industrial high tech processes. But I'll be happy
to be proven wrong...

The structural foams I have looked into have an equal or higher density
than fir or WRC. The one usually used for marine applications here in
Scandinavia, Divinycell, is available in a lot of varieties with
densities (SI-units) ranging from 0,38 (2,4 lbs/ft3) up to 2,5 (15,6
lbs/ft3) (some even up to a staggering 6,0) – compared to ordinary fir
at 0,34-0,45, WRC at 0,32-0,42 and Paulownia at 0,29-0,36 (numbers from
"Nordens Trä och Träslag" and Richard Jagels articles in Wooden Boat).

Furthermore, foam is an isotropic material (same strength in all
directions), while wood is an anisotropic material, developed to handle
incredible loads in long narrow structures like tree trunks and branches
– or kayaks.

At equal density, wood will have maximum strength in the direction where
it counts (longitudinal) and less athwartships where the loads are
relatively small, while foam will lack some longitudinal strength and
have unnecessarily much athwartships. To compensate you have to use
higher density foam and accept an overkill in all but the longitudinal
direction, or add more fiberglass – in both cases equaling the strength
of the standard wood core layup but with increased weight.

Of course a light foam core kayak will do fine, if you accept that it is
a bit fragile och lacks some of the rugged toughness of a wood core
kayak. Since many of the American wooden kayaks are works of art with a
beautiful wood pattern and a superb finish, that would perhaps to many
builders be an acceptable trade-off. My kayaks, on the other hand, are
often painted, with a functional level of finish and I use them hard,
and need reliability and toughness in bad weather along a rocky coast.
So for now, it's wood for me...