To think about seriously.
"is considering adding" is correct and usable in written English. You could use it when describing a situation in which someone is thinking about taking an action. For example, "The board of directors is considering adding two new members to the team.".
Now Facebook is considering adding an ad-free subscription option.
The board is considering adding one more person.
Here are the programs the conference is considering adding.
Yet his company is considering adding newspapers for three other communities south of White Plains.
(AP) POSSIBLE CLASSIC IN CANADA The N.H.L. is considering adding a Winter Classic for Canadian teams.
But the airline is considering adding four new gates in an expanded terminal at MacArthur.
Now the airline is considering adding other drinks and publications, food and possibly Internet terminals.
I love the desktop app, it’s always running on my Mac. Ludwig is the best English buddy, it answers my 100 queries per day and stays cool.
Cristina Valenza
Retail Lead Linguist @ Apple Inc.