The Core i9-9990XE will be a 14-core processor with 28 threads, a 4.0GHz base clock, 5.0GHz Boost, and a 255W TDP. It's basically a super-binned version of the 14-core 9940X.
Intel is listing this processor as 'off roadmap', meaning it won't come to retail. Instead of selling to end users directly, Intel will offer it to select OEMs via a series of auctions, held once a quarter, with the first auction scheduled for the third week of 2019. This means the price of the processor is not fixed, and will depend on how much each system integrator is willing to pay. We also learned that only three system integrators will be at the first auction.Expect systems based on the 9990XE to be ultra expensive. There's no fixed price but we do know that the Core i9-9980XE already costs $1,979.
Overall, this method means that Intel does not have to commit to volume sales: because these chips are super binned, they likely can only build a few hundred a quarter, hence the one auction per quarter.