Mac – *macOS 10.13 High Sierra Beta* Cannot Resize APFS Volumes on External Hard Drive

I have impatiently updated my Mac to the High Sierra Public Beta and I noticed something strange when I was trying to mess with my external hard drive. I have a 4TB WD MyPassport for Mac and I was planning on partitioning it so I could have half of it to use as a Time Machine and the other half for storage. So, I naturally thought I would reformat the drive as APFS and then partition it so everything is in the same format as my internal hard drive. However, once it was in the APFS format and in the partition drop-down, everything was grayed out from the plus/minus buttons to the resize text box. Down below where they normally display the errors it only said that "This volume cannot be resized." I did also run into the issue where I thought that I would just reformat it back to Mac OS Extended (Journaled) (AKA: JHFS+). In the drop-down for the Erase menu, I was only given the four APFS options as the format. So, being the hard-head I am, I went into terminal and used the "diskutil eraseDisk" option to reformat it to JHFS+, which worked. From there I was able to partition it off and reformat one volume to APFS for Time Machine and use the other for extra storage. What I learned after setting up Time Machine, is that it actually needs to be in the JHFS+ format to work. TL;DR So, I guess my question ends up being: does anyone know why I can't partition a drive that is in APFS format? And why does Time Machine use JHFS+ format if the new native format is APFS? As far as the first question, is it just me or maybe because High Sierra is in Beta and it's just something that hasn't been fixed? And for the second, also maybe because it's in Beta and it's just something that hasn't been updated?

Thank you for everyone's time reading this, I know it was kind of a long one.