Gregg Ludwig writes:

The details are provided in the preamble to the new regulations.
The time with a CFI-Sport will only be credited if that Private Pilot candidate
first secures a Sport Pilot certificate.

In the case where a student starts as a Sport Pilot candidate with a CFI-Sport,
and then switches to the Private track, none of the dual time completed with the
CFI-Sport would apply.

The new paragraph 61.109 (l) explains the training credit that applies for
licensed Sport Pilots (and not student pilots):

"(l) Permitted credit for flight training received from a flight instructor with
a sport pilot rating. The holder of a sport pilot certificate may credit flight
training received from a flight instructor with a sport pilot rating toward the
aeronautical experience requirements of this section if the following conditions
are met:

(1) The flight training was accomplished in the same category and class of
aircraft for which the rating is sought;

(2) The flight instructor with a sport pilot rating was authorized to provide
the flight training; and

(3) The flight training included either—

(i) Training on areas of operation that are required for both a sport pilot
certificate and a private pilot certificate; or

(ii) For airplanes with a VH greater than 87 knots CAS, training on the control
and maneuvering of an airplane solely by reference to the flight instruments,
including straight and level flight, turns, descents, climbs, use of radio aids,
and ATC directives, provided the training was received from a flight instructor
with a sport pilot rating who holds an endorsement required by §61.412(c)."