I wonder if they'll bring back the Randuin's rework that was on the PBE a few months ago. In all honesty it favored some champions more than others, but it was definitely more fighter centric than Tank centric as an item when it was available. The active allowed you to "steal" attack speed from champions that were in the AOE slow (the slow was flat instead of scaling off of bonus armor/mr as well), so it mostly favored champions like
but it was definitely more favorable on these fighters than many of the tanks you see who use the item. It wouldn't really help more caster oriented fighters like
as much though. I think it was a step in the right direction as far as fighter itemization though.
Not to mention that the new BC is actually a really good AD fighter item as it provides ample CDR, AD, and Health as well as armor shred that is useful in supporting your team and amplifying your own damage. We see some champions thriving with this new item:
though for some, the old BC was maybe a better investment for the ability to hold onto Brutalizer for the early game.
These are steps in the right direction, but I do think that more variety in itemization should be explored.
I will say this though. AD fighters don't really need more than one damage item in most situations. Building AD is more efficient than building AP as it affects AA's and abilities alike whereas in most situations, AP only affects abilities. AP bruiser itemization did get a lot better with this overhaul of AP items, but before that it was very weak, and I still don't think it's in a great spot.
With Rumble, Singed, and Diana, you are looking at the champions themselves as to why they are moderately tanky while building AP. Diana has a shield that scales well off of AP and doesn't have heavy mana problems, allowing her to rush Abyssal and Zhonya's early. This coupled with her naturally high hp and armor, make her appear very tanky as she can build AP and resists at the same time, making her a very strong midgame champion. The same is very much true for Rumble as he has no mana and he scales very well with penetration allowing him to build Haunting Guise and the other mentioned items without really sacrificing on damage. Singed hp scales off of mana, making RoA the most efficient item for him. So he gets the most HP for his buck along with a good amount of AP. He can build Liandry's and Rylai's because he receives free resists with his ult.
Looking at other champions you might consider: Chogath, Swain, Vlad, Ryze all have access to great use of RoA or have extra stats in the case of Chogath and Vlad and great sustain/spellvamp in their kits to make them seem tankier, but they are usually just a lot of HP without many resists so are easily blown up if they get caught.
We can look at AD champions and see similar things in some of them where you can see why they can build the way they do. Riven for example is like Diana or Rumble in that she has a shield that scales off of AD which is what you want to build as a fighter. You have Gnar who during his Mega form has a lot of HP, AD, and resists coming in like Singed's insanity potion; allowing him to build Black Cleaver, Frozen Mallet, and Maw without losing out on a lot of tankiness. Fiora, who was more of a Carry, was like Vlad or Ryze with all of the lifesteal and hp regen she gains (this has been since changed with her rework). Garen has 20% bonus resists AND 30% damage reduction on his W allowing him to build very heavily in offense and not be lacking in tankiness (he can be kited like crazy though). Triforce users like Hec, Irelia, or Jax usually can make do with that one damage item and still be really tanky thanks to aspects of their kit and the additional items they end up building.
I DO think that Ad fighter itemization needs to be better optimized with Frozen Mallet being one of the things I feel need a complete rework especially now that slow stacking is no longer possible. I also think that AP fighter/offtank itemization still needs work as in most situations, it's either better to build full tank or full AP and those who can be tanky while building a lot of AP items are exceptions, just like there are exceptions to AD fighters who can amass a lot of AD items and still be fairly tanky. There is a big difference in AD fighters and AP fighters as AP champions usually can't build one AP item and go tank afterwards like AD champions can build one AD item and still be effective when building full tank afterwards.
Sorry for the long post. Peace.