What would be threatening is incorporating Gaza: Gaza is a huge Arab city with a sky-high fertility rate and if you include it in "between the Jordan and the Sea" then a Jewish demographic majority is impossible. But there is no reason for Gaza to be part of that state (and as the June 2007 civil conflict showed, Gaza does not even really seem that interested in being part of a state with the West Bank); its history, political preferences, and economy are completely different. Nor is there any particular reason for Israeli ultranationalists to want it, which is why it was easier to withdraw from 2004 than the religiously significant West Bank. There is no reason that, when a government arises there that chooses peace, Gaza couldn't be a prosperous independent port (with extensive natural gas reserves) separate from both Israel and Egypt. Some argument might exist that Israel would have to pay Gaza reparations to apologize for bombing it repeatedly instead of just unilaterally ending the terror of the al-Qassam Brigades.
This is probably the only form of the two-state solution that would work; anything based on modern ethnic borders in the West Bank really does start to look like a bantustan. Ultimately, the first step on the road to peace will be when the Palestinian Authority (and the Israeli state) acknowledge that people in Yatta and Tulkarm, not just al-Quds, deserve the option to have Israeli citizenship.
So this might be nice from some perspectives as something approximating an easy way out, but there are a number of key flaws with your reasoning here. I think before getting into any of that, though, it is worth noting that even just annexing the West Bank and granting Israeli citizenship to all people in the former Mandatory Palestine excepting the Gaza Strip would yield a nation with 5 million Arab citizens out of a nation of about 12.5 million. Not a majority, of course, but not an insignificant change either, and the Israeli right would probably be severely kneecapped in the short term and have to significantly change long-term.
The first major issue is that the current situation of Gaza is quite simply untenable. Its population density is almost on par with that of Hong Kong and only getting higher. The PA would never consent to a 1 state solution without some sort of solution for this situation, nor should they. The obvious solution is to allow some citizens of Gaza to migrate to the new Israel-Palestine, but this hypothetical state is already over 40% Arab, so at some point that's going to become incompatible with a continued demographic Jewish majority.
The second major issue is that of Palestinian refugees, some 3 million of whom live outside of the former mandatory Palestine, mostly in Jordan, Syria, and Lebanon. It is impossible to overstate the importance of solving this issue; indeed, I'd say a solution is impossible without it. With a 1 state solution as it is usually construed, a single state constituting all of former Mandatory Palestine, this isn't that big of a deal, but if you're still trying to maintain a demographic Jewish majority this is yet another group of people you have to find a permanent solution for that doesn't include settling in the new state.
Perhaps you could have Israel just annex the West Bank unilaterally, but frankly I think that leaving those two issues permanently unresolved would incite just as much international condemnation as just unilateral annexation without extending citizenship.
