Adding an arcane half-caster because there are a divine and primal half-caster is the box filling approach and doesn't demonstrate a need to be done just for being absent. That seems to be reinforced by comments that are similar to smite spells and abilities, and that looks like getting hung up on a single term that didn't matter in 5e up until spell list changes being proposed.
There are also several ways to combine melee and magic to various degrees including multi-classing into classic builds. This gets back to too many different people have too many different ideas on what that class would look like.
I do think the artificer should be added to the PHB, however; and the eldritch knight could stand some improvements. But adding another class or radically altering a class doesn't have a good reason to do so.
I mean 5e has an arcane half caster with an identity. It's called the artificer.
And (at least initially) it's not making the jump to 1dnd. We don't even know if it will ever get ported across.
We know from the comments given in the UA's mentioning the artificer that the devs are aware of the artificer. The class is more likely to have at least some information (such as a side bar on how to adapt it) than to have nothing because of those mentions.
Though I've never thought of the Bard as arcane (more occult), I totally think it should be a half caster.
It seems like they forgot the entire 'jack of all trades' thing and turned it into a wizard with a guitar.
Why do you think bards should be a half-caster? We've already learned the community response to bard spell casting early in 3.0 and still in 3.5 with improvements when that version of bard massively outclassed rangers and paladins in magical capabilities. Especially 3.5 with the improvements to bard songs.
I disagree with how you interpret a "jack-of-all-trades". The concept needs to be adequately skilled in each of those areas to be worth playing instead of restricted in all areas to the point no one wants to play one. 5e did a great job by giving other arcane spellcasters benefits to improve their spellcasting. That results in being a decent spell-caster but no where near the benefits of metamagic or invocations. Definitely not the arcane recovery, spell list access, ritual mechanics, spell mastery, or signature spells that wizards enjoy.
A bad caster is not a jack-of-all-trades. It's just a bad caster. The full caster bard that lacks those other enhancements that improve spell casting keeps them relying on skill benefits and inspiration while being subpar compared to other full spellcasters.
People always propose to diminish the bard by demoting them back to half-caster, but never propose what the other half gets to be. Half casters need something to make up for a disappointing spell progression.
Bards were never half-casters. They were full-casters who weren't as fleshed out as other full-casters. In 2e and 3.x caster level mattered. Bards progressed in caster level correctly for a full-caster. Compared to paladins and rangers who gained spells far slower with even lower spell access and with caster level restrictions bards didn't have. 4e used the powers structure (arcane source) so weren't restricted and 5e they continued to use the full structure.
In 2e, the XP advancement tables and bonus XP rules had bards at a higher caster level than other magic-users so they had significant advantages as a full spellcaster. In 3.x the magical songs and variant spell levels still gave bards near full spellcaster magic even before the PrC's that added more.
Looking at bards when clerics and druids also didn't cast 9th level spells and then comparing them to paladins and rangers as half-casters doesn't stand up to critical reasoning. Even calling them 2/3's casters is looking at 3e but ignoring other editions, ignoring the magical song contributions, ignoring the caster level rules, ignoring the spells that varied with spell level based on class, and ignoring PrC's that improved spellcasting for bards further.
