EDIT 2020/03/17 15:15 (CET): as of today, we discovered that OnePlus revamped their OnePlus Forums where you can see the new logo. The logo that we posted yesterday (scroll down to check it out), is most likely not the only variant. There's a black and red variant, as you can see on the OnePlus Forum. This is the red variant:
Every company goes through a change in their brand's visual identity, which usually comes with a shift in focus as well. Maybe this marks a new beginning for OnePlus, as this is the first time OnePlus has opted to refresh their logo:
The most obvious change is the removal of the iconic red colour, as well as a tweak to the "1". Upon closer inspection, the "OnePlus" typeface has also changed, along with the size of the "+".
As a side note, OnePlus has been moving away from using red in their products for quite some time now (even though the OnePlus 7 was sold in a red colourway). If you remember, OnePlus used to have red batteries inside their phones, but stopped from the OnePlus 3 onwards, as you can see in this JerryRigEverything video:
They used the yellow colour in the OnePlus 5, but Zack (yep, his name's Zack, not Jerry) is still disappointed that it's not red anymore:
To many people, the new logo looks like a bland imitation of the old, more vibrant one. The old logo, thanks to the use of the iconic OnePlus colour, personified their "Never Settle" motto - whereas the new logo just looks like a change for the sake of a change.
People have reacted differently to this logo refresh - some perceive this as a more matured OnePlus, while others claim this is an unnecessary change, and that the new logo looks like something that was made quickly by an amateur looking for some extra cash.
Check out Pete Lau's (OnePlus' CEO) forum post, where he talks about the motivation for this new brand identity.
GizChina also wrote an article about this, in which they found that the trademark application for this new logo had been filed way back in November 2019, and was only recently granted. They quote an article from ITHome (it's in Chinese, but you can use Google Translate) to confirm this finding.
Note: This logo is a rumour for now, as OnePlus hasn't officially announced it. However, given how the forum post (linked above) also has the "1" in a similar font, and the trademark application also shows the new logo, we're fairly confident in