We know that Israel wants to ethnically cleans Gaza. They are openly calling for that (and worse). Their plan is to push them all into the northern Sinai (I guess the irony of pushing a slateless people to wander for years in the Sinai desert as been lost on the government of Israel).
Egypt has ruled this out. But not just because they are a poor nation that doesn't want to support millions of refugees. It's because of what has already been happening in the Sinai.

Since 2011, the Egyptian military and police have battled ISIS-affiliated militants in North Sinai governorate. Sparsely populated, and with roughly half-a-million residents, this northern part of the Sinai Peninsula that borders Israel and the Gaza Strip has been a historically marginalized territory, separated from the rest of the country by the Suez Canal. Thousands have been arrested, and hundreds have been disappeared in the past six years since the conflict escalated in 2013. Tens of thousands of residents have been forcibly evicted or fled their homes due to ongoing violence.
This report documents how the Egyptian military and police have carried out systematic and widespread arbitrary arrests—including of children—enforced disappearances, torture, and extrajudicial killings, collective punishment, and forced evictions—abuses it has attempted to conceal through an effective ban on independent reporting. The military has also possibly conducted unlawful air and ground attacks that have killed numerous civilians—including children—and used civilian properties for military purposes. In addition, it has recruited, armed, and directed local militias, which have themselves engaged in serious rights violations, such as torture and arbitrary arrests, often exploiting their position to settle personal scores.

More than 3,000 Egyptian security forces have died fighting this insurgency. The group brought down a Russian airliner that crashed in Sinai, killing 224 people. In November 2017, more than 300 Sufist worshippers were killed and over 100 injured in a terrorist attack on a mosque west of the city of Al-Arish.
So imagine what will happen when 4 times the current population of the region get suddenly displaced and pushed into the Sinai.