As others already said, PA stated they had no plans to increase the max amount of char slots at this time. 28 classes or not, this means we should assume there won't be an expansion unless explicitly stated otherwise in advance of season. 
However I agree with VikingDad, there is no harm in just waiting out the patch notes and then deleting the char after if you had plans to do so. The first days of season are always far too crowded anyway. 

You probably don't know, but deleting characters is not a good solution. You lose everything you have gained with this character: quest counter, family fame, energy, skill points (easy skill points if it's a season character, season give you almost 1000 SP and tomorrow it will be max for all skills), inventory slots (rewards char bound from season) and, of course, the time you spend with this character.

So the case is simple: no more slots (yes slots, because now season requires two slots) = no possibility to play for the season, and for a significant percentage of BDO players, only the season matters.

i alrdy deleted my previous season alt  wasnt hard  didnt do many quests    i do the same quests every season to lvl to 61   as for family fame.. ill get that back anyways  skill points  ill get that back anyways   inventory slots   we get thoise back from doing season again  not an issue  and season doesnt REQUIRE 2 slots  it only REQUIRES one  u choose if u wish to timepiece  u can always delete the timepiece if u dont want to use it if ur alrdy maxed  did it last season  will do it again this season  0 issue at all

im guessing the main reason why no plans past 28 slots atm is the end game menu 

its exactly sized for 28 characters to be shown

they probably havent coded it to show more and thus no plans to increase untill they do

just my theory tho

I know its not a great solution, but it is the solution we have available. If the season char is more important than the old char, then its a good trade off.

If you have an alt that was made before season (which is a given as there were not 28 seasons yet), some of them may be below level 61, with possibly significantly less SP than a new season char could have. Season chars get a lot of freebies as well, which ends up in many cases more effective than a below-61 alt that was only used for storage before. Aka, if you have lower chars that you did not put in much effort on, doing a season speedrun will net you a higher overall outcome in all the fields you mentioned (with exception of energy, though that will restore quickly enough as well). It's simply a matter of priorities. If some people play only for season (which I personally dont understand why they would, but thats their prerogative) then they can decide their priorities as well.

As time continues and after every season I began to be less and less interested. Even if the rewards were to be considered. To remedy myself that I had made kind of an unorthodox decision:

Level a character I was already familliar with and enjoy playing as. Level this character on a different skill build to try it out. Example: I've made a second DK to try it out on succession once and stick with it. My first DK(and one of my 2 mains) is on awa.

Level up the second dk on the seasonal server and invest as little as possible in it. I mean little invetory space and weight limit from loyalty points. Why I say as little as possible? Because it's better than not investing any resources. Get it to full PEN tuvala. You can still choose to invest nothing, but one may find himself hard handicapped. I used fughar's timepiece to reroll in the end to another class and gave the gear to one of my older characters. I didn't bother purchasing a season pass in almost all seasons, save for one when drakania was released for the first time. I had pearls to spare anyway.

Regardless of this small amount of resource investment I still found it rewarding, because I transfered the gear to another character. I wasn't going to keep the character and made my decision. I always save 1 or 2 vacant char slots for the future. It takes me usually average around 3 days of total playtime on that seasonal character to get it to full PEN tuvala. Every next season (after corsair was new) I get easily a full set of max enhanced tuvalla, because I had figured out how to progress with ease. I found success time and again in my "enhancing doctrine" I stick with it nonstop. Lessons were learned ;) .

So far I have seen in pattern, they only increase the max character slots with the release of a new class.
So I don't think there will be a 29th character slot for next season. But character slot expansion coupons (up to said max) are regularly for sale, mainly during seasons.

july 27th   season: dawn of dragons  no new class   drakania got her awakening   28th slot added  

so a new class isnt required to add a slot

theyve done that at least 1 or 2 other seasons that i can remember 

im pretty sure it has to be new season OR new class   just new classes tend to get released in conjunction with new season as its better for PA since everyone will be trying season anyways and new class hype always goes crazy for pearl purchasses 

Also the aformentioned sale on the character slot coupon ends in 22hours.

So it would be really nice to know prior to servers going live after maintenance.

i dont think OP will lost so much to delete his lanh 49

of course if he bought outfit for all his waifus he may be very complicate