I created an automated workaround but still don't understand why it fails in udev :

1- Copy 97-hid2hci.rules :

cp /usr/lib/udev/rules.d/97-hid2hci.rules /etc/udev/rules.d/

2- Remove those lines in /etc/udev/rules.d/97-hid2hci.rules :

ATTR{bInterfaceClass}=="03", ATTR{bInterfaceSubClass}=="01", ATTR{bInterfaceProtocol}=="02", \
ATTRS{bDeviceClass}=="00", ATTRS{idVendor}=="413c", ATTRS{bmAttributes}=="e0", \
   RUN+="hid2hci --method=dell --devpath=%p", ENV{HID2HCI_SWITCH}="1"

3-Create /usr/sbin/dell-bluetooth and make it executable :

#!/bin/bash
DEVPATH=/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.6/2-1.6.2/2-1.6.2:1.0
HID2HCI_SWITCH=1
/usr/lib/udev/hid2hci --method=dell --devpath=$DEVPATH > /dev/null 2>&1
exit 0

4-Create /etc/systemd/user/dell-bluetooth.service :

[Unit]
Description=Fixes bluetooth on some Dell systems with Kernel 4.14 at boot

[Service]
Type=oneshot
ExecStart=/usr/sbin/dell-bluetooth
TimeoutSec=0
StandardOutput=syslog

[Install]
WantedBy=multi-user.target

5-Create /etc/systemd/user/dell-bluetooth-resume.service :

[Unit]
Description=Fixes bluetooth on some Dell systems with Kernel 4.14 at resume
After=suspend.target
#After=systemd-suspend.service systemd-hybrid-sleep.service systemd-hibernate.service

[Service]
Type=oneshot
ExecStart=/usr/sbin/dell-bluetooth
TimeoutSec=0
StandardOutput=syslog

[Install]
WantedBy=sleep.target

6- Enable those two services :

systemctl enable /etc/systemd/user/dell-bluetooth.service
systemctl enable /etc/systemd/user/dell-bluetooth-resume.service

7- Reboot (enjoy)

Funny thing, bluetooth on my Dell only started to work after the update to 4.14, before it didn't work at all and would crash network-manager/gnome-control-center.

Problem also reported on Manjaro with kernel 4.14 and 4.15.

Apparently I used two maniphest IDs in that change -_-

Solus Budgie
Kernel 4.16.7-66.current
Host: M15x A07 (Alienware/Dell)
CPU: Intel i5 M 540 (4) @ 2.528GHz
GPU: NVIDIA GeForce GTX 260M

ikey,
installed https://ring0.solus-project.com/unstable/b/bluez/bluez-5.48-22-1-x86_64.eopkg and rebooted as you requested.

peter@erma ~ $ sudo usysconf run -f
[✗] Reloading udev rules failed

This laptop does not have a Bluetooth device as running the app says: "No Bluetooth Found. Plug in a dongle to use bluetooth."
This is correct to my knowledge.
Main laptop, M15x A08, does have Bluetooth, which works but running Kernel 4.9.98-88.lts

OK I need this tested against current as that seems to be where the issue is. Need the sudo journalctl -ae after that usysconf failure too

Laptop with issue is running Kernel 4.16.7-66.current .
Here's my haste report: https://hastebin.com/evevovihog

FYI, I tested bluez 5.48-22 (and disabled my previous workaround) : log is filled with those errors :

mai 07 07:55:44 dell-laptop upowerd[773]: unhandled action 'bind' on /sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.6/2-1.6.2/2-1.6.2:1.0
mai 07 07:55:44 dell-laptop upowerd[773]: unhandled action 'unbind' on /sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.6/2-1.6.2/2-1.6.2:1.0

So the patch is not working on my system.

Can I get an update from someone with one of these cards? thanks.

On kernel 5.0.7 bluetooth mouse works fine after reboot and no errors logged (still must have /usr/lib/udev/rules.d/97-hid2hci.rules /etc/udev/rules.d/hid2hci.rules modified as described).