So you can not get in to "SafeMode" ?
You could rescue you're device if you enter safemode ....
Hold Power and home untill device reboots , the moment the "Apple Logo" appears , as soon as it shows Press and hold the Volume Up button , keep hold of the Volume button untill you see you're device Lockscreen.
Once you are in SafeMode start by disabling CydiaSubstrait and respring , this will disable all Cydia tweaks that rely on Substrait , you're quest now is to find out what causes the bootloop.
Could be a tweak so one by one enable each tweak and respring , do this untill you're device bootloops again.
When device bootloops again , enter SafeMode and remove that last tweak you enabled.
You should now be able to respring with no bootloop !