I do not know whether Manila instead of PH has ever been thought by Japanese leadership.
But it would have been much more feasible than PH itself.
Same goes with my usual "skipping the Philippines". It would have been quite difficoult for the Allies to transform them in a proper threat to Japanese forces. Also, it would have been quite a reasonable option given the Japanese strategy of a decisive battle with the US Navy approaching Philippines to bring relief.
US Navy itself planned that, also.
Therefore, there is little possibility to say that striking Manila would have been impossible or unrealistic. Under many points of view, it is somehow closely linked to the entire Japanese strategic approach of forcing a defensive decisive battle with US Navy.
Now, we know that US Navy wouldn't have sent their entire fleet across the Pacific to bring relief to Philippines forces under siege, but, again, we are reasoning with hindsight because we know that the leadership on the other side, in Washington, knows that it would be suicidal and doesn't do that. So it's a double hindsight: on one side US leadership does know, and therefore doesn't want to, cross the Pacific to bring relief to Philippines.
On the other side, Japanese players perfectly know that the americans know. Therefore, not a single Japanese would think that skipping Philippines and focussing on them would force (or even invite) US to try to move toward them.
Funnily enough, I have just sent a little relief force from PH to Philippines which have been skipped by my enemy (who, also, landed quite massively on Mersing with everything on day-1 and took Tulagi as well immediately).
Now, if you think under the "feasability" constraint, you have that Manila is perfectly possible.
Under the strategic point of view, somehow yes as well (including skipping Philippines altogether and getting them few months later).
If you speak about gameplay, it's up to you and your adversary. To be honest, I wouldn't play against somebody who gets bothered if things take a very different path than they did in history. As mentioned above, I've never found somebody willing to be under those constraints as well when they do bring some disadvantage to them.
Noumea or Tulagi on 7-dec and so on are totally wild and unfeasible. Still, I do not see a major problem in that (note that in one of my two PBEM I am on the receiving end of having had Noumea attacked in the first few days of war). I think that, on the mid- and long-run, things naturally flow in a somehow historical direction. Some operations are inherently nasty, but I consistently found that over time they do not really matter.
The game in which I got Philippines skipped and Singapore directly invaded at day-1, ended before 1942 just to make an example.
The one in which I got Noumea attacked early (I think 10th dec but I might be few days wrong), it's going on and it's still at the beginning. But I just sank Hosho, trapped 1,000AV in Java and hit multiple times the whole 2ndKB (Akagi/Kaga/2xCVL/2xCVE) with no major losses (few DDs).
So, also in the short-run, some wild initiatives can happen but the whole balance doesn't really change.
Just to make another example of wild Japanese moves to much allied horror. I landed on 28th Jan with 3 divisions coming from Java in... Port Augusta. I did a roughly 150hex trip with 3 embarked Divs plus support units and attacked Port Augusta from South.
Now it's few months later and the last Allied base in the area, Sidney, is falling.
It's not only 7-dec which can go wild.