Why did Korach pick *now* to rebel?

Rav Yonasan Eibeshutz, in Tiferes Yehonasan, considers why Korach decided to initiate his rebellion just now, after the sin of the meraglim. His answer is that the penalty for that sin was a 40 year stay in the wilderness. Beforehand, Korach thought he could wait it out. After all, it was only 11 days until they entered the land, and for saying lama hareota, it had already been decreed that Moshe would not enter the land. Therefore, he would have his chance at glory, once inside the land. Or alternatively, we was concerned with his role in carrying the Aron, which was fatal to those who were not worthy. But for a short time, this was no concern, and there would be no carrying of the Aron once they entered the land. Therefore, once these 40 years were a concern for him, he came up with this strategy.

There are some interesting points in play. For example, how exactly do we take this midrash from Sanhedrin 111a, that it was decreed that Moshe would not enter the land. Rashi cites it on Shemot 6:

Now you will see, etc.: You have questioned My ways [of running the world, which is] unlike Abraham, to whom I said, “For in Isaac will be called your seed” (Gen. 21:12), and afterwards I said to him, “Bring him up there for a burnt offering” (Gen. 22:2), yet he did not question Me. Therefore, now you will see. What is done to Pharaoh you will see, but not what is done to the kings of the seven nations when I bring them [the children of Israel] into the land [of Israel]. — [from Sanh. 111a]

עתה תראה וגו': הרהרת על מדותי, לא כאברהם שאמרתי לו (בראשית כא יב) כי ביצחק יקרא לך זרע, ואחר כך אמרתי לו (שם כב ב) העלהו לעולה, ולא הרהר אחרי, לפיכך עתה תראה. העשוי לפרעה תראה, ולא העשוי למלכי שבעה אומות, כשאביאם לארץ:

and the idea of punishment for this early reluctance in his mission fits well with the pesukim and midrash in perek 4 on shelach na beyad tishlach. But what of the pasuk in Chukas of the response to shim'u na hamorim, and the midrash (on Bemidbar 20:12, also brought down in Rashi) that it was only for this and no other sin? I'm inclined to read this as foreshadowing of the future downfall, just as Rashi discusses on Shemot 1:22 the astrological prediction that Moshe's downfall (of not entering the land) would be through water. There might be other ways of resolving this conflict, or apparent conflict. Maybe these are conflicting midrashim, but how does a midrash conflict with a pasuk? But even if such was the gzeirah, was Moshe even told of this at this point? Was it well-known to kelal Yisrael? Why then does Rashi cite the Midrash (on Bemidbar 11:28) that Yehoshua was upset by the prophecy that Moshe would die and that Yehoshua would take them into the land? Though this was still slightly before the spies...

Another interesting point is that we indeed see the idea here of people rebelling while upset about not entering the land. Thus, Datan and Aviram say:

יב וַיִּשְׁלַח מֹשֶׁה, לִקְרֹא לְדָתָן וְלַאֲבִירָם בְּנֵי אֱלִיאָב; וַיֹּאמְרוּ, לֹא נַעֲלֶה.	12 And Moses sent to call Dathan and Abiram, the sons of Eliab; and they said: 'We will not come up;
יג הַמְעַט, כִּי הֶעֱלִיתָנוּ מֵאֶרֶץ זָבַת חָלָב וּדְבַשׁ, לַהֲמִיתֵנוּ, בַּמִּדְבָּר: כִּי-תִשְׂתָּרֵר עָלֵינוּ, גַּם-הִשְׂתָּרֵר.	13 is it a small thing that thou hast brought us up out of a land flowing with milk and honey, to kill us in the wilderness, but thou must needs make thyself also a prince over us?
יד אַף לֹא אֶל-אֶרֶץ זָבַת חָלָב וּדְבַשׁ, הֲבִיאֹתָנוּ, וַתִּתֶּן-לָנוּ, נַחֲלַת שָׂדֶה וָכָרֶם; הַעֵינֵי הָאֲנָשִׁים הָהֵם, תְּנַקֵּר--לֹא נַעֲלֶה.	14 Moreover thou hast not brought us into a land flowing with milk and honey, nor given us inheritance of fields and vineyards; wilt thou put out the eyes of these men? we will not come up.'

Perhaps we can read this as an emotional reaction of learning they would die in the wilderness instead of settling the land. This would then be an emotional reaction rather than a cold calculation.