While Sony stopped updates to their PlayStation Portable and PSPgo handheld console XML Updaters back in 2014, in PlayStation Vita News following the previous PS Vita OFW revision and PS3 4.89 Firmware Update earlier today a PS Vita System Software / Firmware 3.74 Update was also pushed live. 
Needless to say, it's advisable NOT to update as many in the PlayStation Vita Scene got a PS Vita or PlayStation TV to do fun stuff like jailbreaking, running exploits and homebrew on the handheld console.
Download: PS Vita Firmware 3.74 Update (US) / PS Vita Firmware 3.74 Update (EU) / PS Vita Firmware 3.74 Update (JP)
While Sony's official page isn't updated with this latest PlayStation Vita 3.74 OFW version yet, many including ultimate_presi on Twitter speculate it may be due to the revamped PlayStation Plus service that is scheduled to arrive this June since temporarily disabling PS Plus subscription stacking last month.
Update: Below is the official PS Vita System Software Update 3.74 changelog from Sony's Page alongside some previous articles sorted by date with the oldest first:
Version 3.74
Signing in to PlayStation Network now requires a device password for enhanced account protection.
Account creation for PlayStation Network and some account management features are no longer available on the console. Use your PC or mobile browser to use account management features with improved performance, speed, and safety.

H-encore2 on 3.74
Rough translation: We are really lucky that h-encore2 works on 3.74.
New PS3 4.89/PS Vita 3.74 System Software Update

Download: PS Vita Firmware 3.74 Update (US) / PS Vita Firmware 3.74 Update (EU) / PS Vita Firmware 3.74 Update (JP)
While Sony's official page isn't updated with this latest PlayStation Vita 3.74 OFW version yet, many including ultimate_presi on Twitter speculate it may be due to the revamped PlayStation Plus service that is scheduled to arrive this June since temporarily disabling PS Plus subscription stacking last month.

Version 3.74
Signing in to PlayStation Network now requires a device password for enhanced account protection.
Account creation for PlayStation Network and some account management features are no longer available on the console. Use your PC or mobile browser to use account management features with improved performance, speed, and safety.
- PS Vita and PS TV Trinity Exploit for Firmware 3.69 / 3.70
- H-Encore 2 Kernel Exploit for PS Vita Firmware 3.65-3.71
- DSLL-MDR72: PS Vita / PS TV 3.71 & 3.72 Downgrader to 3.65 Firmware

H-encore2 on 3.74
Rough translation: We are really lucky that h-encore2 works on 3.74.
New PS3 4.89/PS Vita 3.74 System Software Update
- FinalHE_v1.92_win32.zip (9.1 MB)
- modoru.vpk (modoru v2.3 - Added compatibility for FW 3.74)
- VitaDeploy.vpk (VitaDeploy v1.0.1 - For firmware 3.60-3.74)
- HENlo (WIP) / HENlo Live Demo / Project Amber HENlo Fork & Manual by RealYoti / HENlo Live Demo via skgleba / HENlo Live Demo (Fake Firmware Version) via RealYoti