I've moved this theme, as, to my opinion, it's not just speculation, but a development, that actually started quite early
during WW II.
The type of the "light bomber", as exemplified by the Fairey Battle, Bristol Blenheim or Mitsubishi Ki-51 Sonia often proved to
be too slow and vulnerable in the standard bomber role. So, the task of those types were often taken over by fighter bombers.
Neverthless, the light bomber saw new developments, but with a somewhat different role: Low level bombing, ground attack
and strafing, more emphasizing fixed armament, making those types more suitable for the role as heavy fighter/night fighter,
too. Examples may be the Douglas A-20 Boston, deHavilland Mosquito, or perhaps Messerschmitt Me 210/410. After WW II,
most fighters could be used as fighter bombers from the start, I think, leading to types like the MDD F-4, that completely took
over the task of the former light bombers like Martin B-51/EE Canberra. At least with regards to external appearance, the light
bomber had completey merged with the fighter, think of the Republic F-105 (a bomber with a fighter designation), the Panavia
Tornado, or the F-111, and at least the latter hardly fit into the "light" category anymore, but was subject of being developed
into a fighter (just as the Tornado, though that still has size and shape of a standard fighter).
The list of bombers, which were used as fighters, developed with both tasks in mind, or at least giving the basis, probably is much longer:
- Jakowlew Jak-28
- SNCASO Vautour
- TSR.1
- Tupolev Tu-98/Tu-128