I run the retext package without having gconf or qt5-webkit installed and didn't notice any issues. Apparently, these two dependencies could be made optional.

gconf was used to set the icon theme, but it is optional since September 2015 [1].

For QtWebKit, the release notes of retext 6.0 [2] say (commit 3b14932 [3]):
> The QtWebKit dependency is now optional (though still recommended).

Despite the recommendation, it would be great if it could be made optional, since the package with its dependencies is quite huge for basic text editing.

$ pacman -S qt5-webkit
resolving dependencies...
looking for conflicting packages...

Package (6) New Version Net Change Download Size

extra/qt5-declarative 5.7.0-2 16.74 MiB 3.17 MiB
extra/qt5-location 5.7.0-1 2.97 MiB 0.60 MiB
extra/qt5-sensors 5.7.0-1 0.86 MiB 0.15 MiB
extra/qt5-webchannel 5.7.0-1 0.18 MiB 0.06 MiB
extra/qt5-xmlpatterns 5.7.0-1 6.30 MiB 1.15 MiB
extra/qt5-webkit 5.7.0-1 37.05 MiB 8.76 MiB

Total Download Size: 13.89 MiB
Total Installed Size: 64.10 MiB

[1] https://github.com/retext-project/retext/commit/2560906dd100329f65628f4bbf1df101dbca28f6
[2] https://github.com/retext-project/retext/blob/fe8a4576ccb7ae34d30e3af48ac3c53315db527e/changelog.md
[3] https://github.com/retext-project/retext/commit/3b1493241b832bc329b6f8e596a66a8e9416d9bc

Additional info:
* retext 6.0.1-1