We started to work on the table selection feature. Since it is a bigger task that will be delivered over multiple releases we split the task to the following sub-tickets:
Tracked here: https://github.com/ckeditor/ckeditor5/issues/6285.
Tracked here: https://github.com/ckeditor/ckeditor5/issues/6297.
Right now, as defined in https://github.com/ckeditor/ckeditor5-table/issues/3 we support only "a custom table selection". This means that it's possible to place the selection inside table cells, but you cannot select an entire table cell and, most importantly, more than one cell at a time. Which means that you cannot select rows and columns.
CKEditor 4 implements a custom cell/row/col selection (you check it live e.g. on https://ckeditor.com/ckeditor-4/#document). It works incomparably better than the native selection which in all browsers (without maybe Firefox) is just useless.
What we need is something very similar to what CKEditor 4 offers.
Some POC of fake selection in tables with current post fixers, table model (with block content), etc:

The above POC is implemented as custom class wchich tracks selection on table in three different modes:
I have some UI/UX questions (cc @oleq, @dkonopka) on how we're going to implement this.
In https://github.com/ckeditor/ckeditor5-table/issues/1#issuecomment-392034926 @oleq defined how merge cell option should behave. But do we fancy another modes besides "block" mode? I've implemented "row"/"column" modes as it was simple addition to the "block" mode. Also I've seen this on other text-edtiors (like LibreOffice):

ps.: Side note - right now I don't have strong opinion/idea how to translate this fake selection to commands as such selection is not possible in the model due to selection post-fixer. Right now I'm leaning towards TableSelection plugin which might be used by the TableToolbar to determine which buttons/options render since with multple cell selection some options may be changed, like:
The merge cells button should be a simple button that merges selected cells, nothing more.
As for the column/block selection feature, I think we can live without it (ATM). Let's talk about it and find out if it makes sense for us in the follow-up issue, OK?
When would this feature be available for tables?
Do we know when this feature would be available? I have a requirement where users want to paste to part of the table from excel.
The branches with a preview were updated to i/3202 in ckeditor5-table and ckeditor5-engine repos. Old branches (t/63) were removed.
Would be nice to have this handled by the inspector: https://github.com/ckeditor/ckeditor5-inspector/issues/68.
Done :) It can be tested in the nightly docs: https://ckeditor5.github.io/docs/nightly/ckeditor5/latest/features/table.html