I will take a stab at answering some of your questions.

For the current trend in foil shapes look at the BIM XJ. The foil shape they call out, was the hot foil in articles 3-4 years ago.

I always think of the Elliptical tips as maintaining lift while reducing area (and drag). This is the theory. However they only really work in undisturbed fluid and where there are no nearby (~50 cm) boundaries. Boundaries can include the bottom or thermal layers.

There was some testing done in the 40-50's on tip shape. The flight testing of elliptical tips did not show the benefit promised by theory and wind tunnel. The tapered sections (which would include trapezoidal) worked about as well. I was shown a test report from North American Aviation. I remember thinking, all the wing shapes look to be within margin of test error. Tapered sections won because they promised some improvement, saved weight, and were almost as easy to build as a straight section (for rib and skin construction)

Elliptical and tapered sections are harder than straight sections for the homebuilder to build right. The best method I found was to use a CAD/CAM program to build a file for a CNC router to cut cores. This feel apart when the CNC router owner got a big contract. You could also build a plywood skin and rib foil to use as a plug for a mold.

In summary, in deep smooth water and design wind speeds, an elliptical high aspect ratio board will probably outrun a square low aspect board. under other conditions there will be little to no difference.

Finishing your hull and foils to a near perfect condition might have a bigger impact.