[General Topics] yourrealking:
I finally succeeded it, after literally months of trial and error! So, I am writing this post in hope that someone who wants to install Oreo on Life One X in the future would find this post through Google search.

Here are the steps.

0. From this page (https://xdaforums.com/android/development/rom-official-mados-wiko-fever-clones-t3762800), download the TWRP recovery and the madOS Oreo ROM.

1. Download the BLUEFEVER ROM from this page (https://www.npcglib.org/~stathis/blog/2016/04/13/turned-blu-life-one-x-wiko-fever-4g/).

2. Download the SP Flash Tool from the page above or through Google search. The version I used was 5.1812, which seemed to be the latest version.

3. Download the Universal ROM from this page (https://xdaforums.com/android/development/flashable-wiko-fever-stock-marshmallow-t3720484)

4. The critical things is you should not flash the Universal ROM as it is, because that bricked my One X. You need to copy "preloader_l5460.bin" and "secro.img" from BLUEFEVER in step 1 and overwrite them to the Universal ROM.

5. You need to install the Mediatek Driver. I used "MT65XX USB VCOM" driver. I found it using Google search, but forgot where I got it from. But with that name, I think you can find it.

6. Now start the Flash Tool, and and select the download agent in the Flash Tool directory (MTK_AllInOne_DA.bin), and select the scatter file in the Universal rom (MMX BLU), and then select "Format all + Download". Then, this is very important, press the download button BEFORE connecting the phone, otherwise it will not work.

7. Now, turn off the phone (I mean, power off, not just screen off) and then connect it to the PC. If the tool does not recognise the phone, press volume up + down at the same time when you connect it until the device connected sound comes from Windows.

8. Now the tool flashs the rom. Wait. It may take a few minutes.

9. If it is bricked, just leave it for a month until the battery drains and completely turns off, and then try flashing again.

10. Now, boot up the phone, go to Settings -> About and hit the build number several times to enable the developer menu.

11. In the developer menu, enable OEM unlocking.

12. Now, install the Google USB Driver. This can be easily found through a Google search. You need to get the "platform-tools" directory of the Android SDK, which can also be easily found.

13. Now, turn off the phone, and hold volume up + power button. The phone shows tiny menu (really tiny...). The first is recovery, the second is fast boot, and the third is normal. Choose fast boot. Type "fastboot oem unlock". You need to press the volume up button on the phone now.

14. Now the phone is unlocked. Type "fastboot.exe flash recovery twrp_wiko_fever_oreo.img" to flash the recovery.

15. Restart in the recovery using the 13th step.

16. Go to Wipe -> Format data and format the data, otherwise the recovery will not recognise the storage and will not boot.

17. Go to Open Gapps and get ARM64, 8.1, micro. Editions above micro will NOT install with an error message that says insufficient storage.

18. Now connect the phone to the PC. The TWRP recovery automatically mounts the storage to the PC so that you can copy files into it. Copy the mad OS rom ZIP from step 0 and the OpenGapps from step 17.

19. Flash the two using the install menu of TWRP.

20. Done.

I do not use One X as a phone, so I skipped the radio flashing steps. It currently shows the baseband is unknown. If you want to use the phone feature, I think you need to flash the radio img or something using the instructions somewhere in the linked posts.