As per the list for devices to be updated to Android O, those with first major upgrade will most probably get Android P or whatever next upgrade is and those devices with Andoid O being the second major upgrade, will not get the next major upgrade as per Samsung policy
What this means is that if your device has already received an OS upgrade, such as S7 edge which moved from Marshmallow to Nougat, the Android Oreo update will be the last major update and if the update to Android Oreo is your first update, such as the S8 then you will receive the next Android update after Oreo
Thanks for being with Samsung and for sharing your feedback. Sir, Samsung offers you the best value on the product released. Updates are rolling out by time to time for the devices, However it totally depends on the availability and compatibility of the update with the devices. We appreciate your inestimable suggestion. We have noted down your valuable feedback and we will surely share this with our relevant department, any update in this regards will be convey to you via various means of communication.
