Does "it is entirely possible that" require the subjunctive form of the verb following "that"?

For instance, take the following sentence (from a real email exchange):

it is entirely possible that one WebEx is not enough

Is it correct? Should it be

it is entirely possible that one WebEx be not enough

?

My reasoning is as follows:

(1) it is necessary that you be here -->
(2) it is necessary that one WebEx be here --> 
(3) it is necessary that one WebEx be enough --> 
(4) it is necessary that one WebEx be not enough --> 
(5) it is entirely possible that one WebEx be not enough --> 

Is it true that the grammatical context is preserved throughout the entire transformation, starting with a sentence known to require the subjunctive (1) and ending with my example (5) ?

I have performed a few simple Google searches and the results are quite confusing:

• "it is necessary that he be" yields 170,000 results
• "it is necessary that he is" yields 342,000 results
• "it is possible that he be" yields 985,000 results
• "it is possible that he is" yields 4,040,000 results

Of course, no conclusions can be drawn from these results ...

Solution 1:

The phrase it is possible that can be followed by just about any tense you please. The adverb entirely has no bearing on the matter.

It is entirely possible that he was here yesterday.

It is entirely possible he's sitting in the library as we speak.

It is entirely possible that it will rain tomorrow.

etc.

It is necessary that is an example of an indirect command, which I got into some trouble by describing as a form that demands the subjunctive here.

It is possible that, though, is grammatically no different from it's likely that or it's unlikely that, forms which don't necessitate the plain, unconjugated verb (whether that's something you call the subjunctive or the "infinitive minus to").

Solution 2:

Traditionally, "necessary that he be" takes the subjunctive, as it is a demand; "impossible that he be" takes the subjunctive, as it is a counterfactual. The phrase "possible that he is" does not take the subjunctive, as it is neither a demand nor a counterfactual.

Remarkably¹, for "necessary that" and "possible that", most sources used by Google Ngrams get it right:

The phrase "impossible that he ..." is much rarer than either of the above phrases, to the point that I don't trust Google Ngrams's graph because a sentence break often appears in the results I've checked. However, both the indicative and subjunctive moods seem to be used reasonably often with "impossible"

¹ Particularly for a mood which has often been declared dead.

Solution 3:

The reasoning is based on a false premise. Contemporary English, at least contemporary British English, doesn’t use constructions like It is necessary that you be here in other than the most formal contexts. The normal expression would be You need to be here. It follows that It is entirely possible that one WebEx be not enough would also be appropriate only in the most formal contexts, so formal, in fact, that they would be unlikely to be the ones in which a thought such as this might be expressed. The normal way of saying it, again in BrEng, and depending on the time frame, would be It is entirely possible that one WebEx won’t be enough.